Explaining and animating how cloakfish swim

In the two previous posts I wrote about parts of The Book that provide background information about how animals move on Furaha. There will be four double-page spreads showing such themes in The Book, about rusps, spidrids, tetrapters and cloakfish. 

I thought the cloakfish one would be easy, until I decided that it was high time I also made some progress towards a short CGI documentary I wrote about earlier, the one with cloakfish biodiversity as its main subject. That is a very big job and it is quite possible that I will fail on the programming side. But nothing ventured, nothing gained, so I went ahead and put some hours into Matlab programming. My strategy to design diverse cloakfish is to write editors that allow shapes to be designed with ease. The programmes then proceeds to make ‘3d meshes’, the basic working material for 3D design. How to get from meshes to nice photorealistic images is another story altogether. 

Click to enlarge; copyright Gert van Dijk

These are the editor screens. The user places control points here and there, which are then connected by a spline function. This results in nice smooth curves, useful for organic shapes. Panel A shows the body designer with a default shape. The inset shows a separate window controlling cross-sections of the beastie. By changing both shape and cross sections interesting forms can be produced. Panel B is the cloak editor. Apart from determining the shape of the cloak it also allows control over cloak movement, such as number of waves, wave amplitude, cloak curvature, thickness, etc. Panel C does something similar for the four front fins, and panel D shows the resulting output for the default shapes. 

Click to enlarge; copyright Gert van Dijk

With a few minutes’ worth of tinkering, you get this relatively slender cloakfish, probably a reasonably fast swimmer. 

Click to enlarge; copyright Gert van Dijk

Or this short and bulky ‘short-sleaved cloakfish’.

Click to enlarge; copyright Gert van Dijk

Or even this highly derived cloakfish, in which the cloaks are no longer ribbons, but shaped like penguin wings. They function in much the same way. 

 But the main point of this post was to show how the cloaks move. To do that, I had a look at the literature, and I found some papers on knifefish, but to my surprise more papers about artificial robot fish with similar fins. Apparently, people all over the world are working on robot fish, which is nice. Less nice is that some work at defence institutes, so what are they preparing for? Killer fish robots? Must we really? 

Click to enlarge; from: Liu, Curet. Swimming performance of a bio-inspired robotic vessel with undulating fin propulsion. Bioinspir. Biomim. 13 (2018) 056006 1748-3190/aacd26

Anyway, here is an example of robot ribbon fin design. The artificial cloak design followed exactly the same reasoning as my virtual cloakfish designs. Such papers make a distinction between ‘oscillation’ and ‘undulation’. If a cloak, ribbon or fin swings side-to-side as a whole, the word ‘oscillation’ is used, and when waves travel along the length of the cloak, it is ‘undulation’. But the distinction is not all that clear; it depends on the number of waves travelling along the cloak. If there is less than one wave on the cloak or fin at a time, then the movement largely concerns the fin as a whole, so the movement edges towards oscillation. Here is a YouTube film explaining the difference. 

Pure oscillatory sideways movement are useless, because they do not propel the beast forwards. The animation above shows such an almost pure sideways movement of the cloaks. The movement would push water away from the cloak, resulting in a force towards the attachment of the cloak (the ‘dagger’). In knifefish, with just one cloak underneath the body, this force ‘heaves’ the body up. With four cloaks, the dagger will not be going anywhere, so this is just a waste of energy. We want water to be pushed backwards. The cloaks push water backwards when its parts are at an angle to the direction of movement. These parts produce forwards thrust. 

Let’s equip our default cloakfish with exactly one wave per cloak. One half of that wave will be angled towards the left, and the other half towards the right. Both produce sideways forces, but these should cancel one another out. The robot designers reported that the robots swam nicely with just one wave per cloak. Mind you, the robots usually had just one cloak, like the knifefish. 

The animation also shows one other trick: if you look closely, you can see that the cloaks do not sway much at front, and the amplitude of the wave increases towards the back of the animal. I borrowed that from real biology, as at least rays and knifefish do this. 

Let’s now equip our knifefish with 2 waves per cloak. The parts of the wave that are useful for swimming are now at a steeper angle towards the direction of movement, nearing perpendicular to it. I thought that this should increase the propulsive force a lot, but work on the robot fish did not agree. The velocity did not increase much, but the robot was more stable, which is intriguing. Real knifefish have more than two fins on their ribbon fins at one time, so there must be an advantage in that. 

Click to enlarge; from: Blevins, Lauder. Rajiform locomotion: three-dimensional kinematics of the pectoral fin surface during swimming in the freshwater stingray Potamotrygon orbignyi.  The Journal of Experimental Biology 2012; 215, 3231-3241

This image is from a paper about ray fin movement. The fins as a whole move up and down (so they oscillate), while there are ripples along the edges of the fins (so they also undulate). Nature seems to like combinations better than separations. The edges of the fins curl up and down, so they do not move as if there are completely stiff rays in them. 

I decided to build that in too, so here is a ‘curly-cloaked cloakfish’. I like it. One odd thing about these cloakfish animations is that it is not immediately obvious how they work, when you see the movement. It is also not easy to find an angle, when you rotate the objects, from where it is easy to get an immediate overview just how the animal is built. That can be seen as a disadvantage, or, in reverse, as an advantage, because it underlines that we are looking at an alien shape. 

By now, cloakfish ‘evolution’ has progressed to allow a variety of body and cloak shapes. Shapes range from ‘long-sleeved’ cloakfish with long narrow ribbon fins with multiple waves along their surface, to very short star-shaped cloakfish with narrow wings that fly through the water. That is certainly enough material for two explanatory pages in The Book, and should be enough for a short documentary too. But that will depend on me improving my skills as regards merging and smoothing 3D meshes.

Work in progress: A cloakfish documentary, with music!

Cloakfish have featured before in this blog, for instance here and here. With their four undulating fins, the 'cloaks', they lend themselves well to animation. Actually, like some other shapes and ideasm they really NEED animation. The movements of the cloaks are calculated with matlab using trigonometry, and the results is written away as a so-called obj-file and later imported in a rendering program, in my case Vue Infinite.

The animation in this post was one of my last attempts. The movements of the cloaks were calculated with Matlab, which resulted in lots of so-called obj-files that were imported in a rendering program, in my case Vue Infinite. If you look carefully you will see that the cloaks are the only moving part of the animal; that is because the rest is modelled as an unyielding and immobile blob.

The last time I showed such an animation to an international audience was at the TetZoo convention in London in October 2018, where I was given the chance to talk about the Furaha project. Afterwards I met another speaker, Fiona Taylor, who had given a talk on the use of music in nature documentaries. She showed, with examples, how strong music can influence the mood of the documentary, or in fact determine that mood. Here is Fiona's website; she has a very nice blog as well. I recommend that you read part of it, to understand the art and craft of using music for nature documentaries.

We got to talking in the corridors afterwards and she mentioned that, when she saw the cloakfish animation, she starting thinking what kind of music would fit with it. I liked that idea very much; as I have absolutely no musical talents whatsoever, the idea of getting a professional to take care of music was very appealing.

Unfortunately, I was too busy for a year to working on a big project, but that has changed now, so I have starting programming. The new programmes should result in more detail, and in particular in much more control over cloakfish form and movement. Once that is achieved, it should be easy to produce several species of cloakfish and set up scenes. After that, my computer will take over: one minute of film will require 60 times 25, or 1500, images. I would like to achieve a resolution of 1280x720 pixels, but that will depend on how long the rendering takes.

The first item on the programming agenda consisted of better mesh-producing algorithms. A 'mesh', in computer graphics, is a set of connected triangles (or other shapes) that together define a surface. Unfortunately, I cannot make use of ready-made programmes because I have no idea which programme can produce the undulating membranes that define cloakfish movement. I suppose that high-end programmes such as 3D Max and Maya can do so, but one look at their price range is enough to start looking for alternatives (doe any readers know whether Blender can do that?). One alternative, of course, is the old-fashioned hard work approach. Lacking the means to solve the problem using a lazy approach, actual work seemed the only choice left.

I chose to start on another marine animal, a 'crin', a sponge-like sessile lifeform that feeds by filtering sea water. It is simpler to produce. Crins are tube-shaped. Their plankton sieves are hidden away inside the tube. Crins can increase the volume of water they 'harvest' by pumping water actively through its tube. In some form or another they have featured in the Furaha universe from the beginning, even though I never painted one. My present aims were firstly to define it in such a way that I could produce low- and high resolution versions at will; secondly, to deform the body while keeping the mesh structure intact; thirdly, to deform the texture of the animal along with the shape itself. For the connoisseurs: that meant a better understanding of 'UV coordinates' and much better housekeeping of which vertex goes where.  

Click to enlarge; copyright Gert van Dijk

This is an image of the 'Crin Designer', showing how the contour of the crin is initially defined with just a few points, shown connected with blue lines. These are connected by smooth curves, in red, that form the basis of the mesh production. The crin’s 'foot' is supposed to be fastened to a rock or something similar, but here it is just a disc. The tube does not run completely through the animal, but outward appearances are enough for now. I had not realised how much it looked like a wineglass. Perhaps I should call this species "P. grigio"...

Click to enlarge; copyright Gert van Dijk

Here is a high resolution mesh.

And here is an animation, in Matlab, of a low resolution version. The movement worked nicely, even though the water transport should perhaps be in the other direction, with water flowing in at the bottom and out through the top, instead of the other way around. In life, I imagine that crins do not pump water this energetically continuously, but only every now and then.

How about texture control? Here is a test render with a simple texture that allows me to see how the texture responds to the deformations. It worked as intended, so that's good. The deformation is simple and the background is not animated at all, but this is just a test render, after all.

And here is another test, this time with a more natural texture. It looks a bit like an octopus skin, which I like.

Work on the 'Great Cloakfish Designer' progresses nicely. But it will take quite time to get it ready, and only then can I start producing animations, even at a small size that I hope Fiona can work with. We hope to keep you informed of the progress on this blog, and possibly also on Fiona's blog.

The Return of the Common Cloakfish

From time to time I find that my self-imposed restriction on not doing any Furaha work except working on The Book begins to chafe. I know that animations cannot feature in a book, but they are fun if very time consuming, and that holds for blogging too. So I gave myself a short vacation from painting and went back to an old favourite: cloakfish. The type of cloakfish shown in this blog previously as well as in this particular post is by now a primitive one. More evolved cloakfish have shown a considerable adaptive radiation: bodies were squeezed, cloaks either merged with the body or were stretched, etc., etc. There are now 'short sleeved' cloakfish as well as 'long sleeved cloakfish'.  The protocloakfish I will show in this post is a long sleeved one: the cloaks are considerably longer than they are wide.

The novel feature I wished to explore had to do with cloak movement. Until now, the cloaks moved with waves undulating backwards over the fin, pushing the animal forward. If you look closely at squid and cuttlefish, Earth's own indigenous aliens, you can at times observe that there seem to be several waves travelling over their fins at the same time: let's call them major waves and minor ones, and each set seems to be controlled independently. Here is a YouTube video showing squid movement: most of the time you see just one type of wave, but at times the pattern changes. I would not be surprised to learn that fin control in cephalopods is neurologically quite complex. I really must look up what I can find about that in my books on cephalopods (yes, I have more than one book on cephalopods: every self-respecting geek with an interest in speculative biology should devote part of a book shelf to cephalopods).

To start with, here is a simple animation showing just one wave pattern; let's call these the major waves. The waves are fairly large, meaning their amplitude is large and so is their length: they take up a sizeable portion of the cloak. The gait of the four cloaks is the 'opposite' pattern, in which the waves of neighbouring cloaks approach one another. The red ball is there only as a reminder where the 0,0,0 point is in this virtual 3D space.

The next phase, above, is of course to show the minor waves: there are more of them and they travel faster along the cloak. Mind you, I have not considered the effects of interacting waves on propulsion much yet; my first suspicion is that they can augment one another, but if they can do that, they can probably also hinder one another.  Hm. This will require thought.

Anyway, programming and visualising all this makes it difficult to think of everything at once, so first let's see what the combination looks like. Here it is. I like it; it is complex and looks organic and fairly odd. The movement reminds me of that of nudibranchs (if 'nudibranchs' mean nothing to you, just use that word to search for images in Google. You may find that you have to make room next on your book shelf next to the cephalopod section; nudibranchs look delightfully alien too.)

   
Very well, let's now assemble a whole cloakfish with this new swimming pattern. The body assemby is modelled very roughly here, without any details at all. As you can see, I wondered whether cloakfish might be able to change colour? I do not see why not, so here is my first attempt ever of depicting a Furahan animal changing colour. For the technically minded, the colour changes require  two steps: first I wrote a simple Matlab program to interpolate colours between two images, resulting in a new set of images showing intermediate changes. Second, I wrote a python script to get Vue Infinite, the programme I use to render the image, to load a different image to use as texture for each frame. In this case the changes in colour are not that big, but you can probably envisage cloakfish changing colours in much more radical fashion.

Here is the colour change again, first in close-up, and then in the form of a short scene of a common cloakfish making its way over a reef. Those who are very observant will see that the alignment of the body with the cloak-and-dagger assembly differs between the two animations. The reason for that is simply that I forgot to rotate the body around its longitudinal axis by 45 degrees. The reef scene shows the correct position of the body.

Anyway, clearly and obviously, animations have their own attraction and advantages, such as showing colour changes. How can I ever show a cloakfish changing colour on a painting?    

Unveiling cloakfishes' cloaked filters

I stopped blogging, so what is this post doing here?

Well, I never said I would stop altogether, and I would return if there was something of special interest to report. Yesterday, I received my advance copy of  'Demain, les animaux du futur' from the authors, Marc Boulay and Jean-Sébastien Steyer. I am quite impressed and will return to write about it, in a week or so. Writing the present post is to get me in the mood again.

A main reason to reduce blogging was to spend more time on producing The Book, and that worked quite well: without blogging, I manage to produce one two-page spread every month, meaning one full painting, accompanying text, scale drawings and usually a minor illustration. At 24 pages a year there is definite progress (and I intend to increase the output). Sadly, Fishes I, II and III together only get one spread, while terrestrial hexapods get many. To illustrate the mechanics of some groups, I have stumbled on a three-spread theme: one spread for explanation, one to show diversity, and one showing a single species in a full painting. Groups that get this treatment are spidrids (half finished), rusps (all done), tetropters (not yet) and cloakfish: half done.

Click to enlarge; copyright Gert van Dijk

The early beginnings of cloakfish are shown here, and the latest instalment of their physique was posted here. Like it or not, that particular form, shown above, has now been scrapped. As you can see I played with putting the mouth in the cone forming the 'snout' of the animal. Well, not anymore. While sketching I drew a cloakfish cut in two and that gave me the idea of making a 'cutaway' version to explain how it works. Unfortunately, that meant that I could use very little 'handwavium'. Without a cutaway drawing I could just write something like this: (imagine an Attenborough-style voice-over) "Hidden from view by the animal's cylindrical body wall, its food rakes, next to the gills, steadily filter the nutritious plankton so abundant in these waters." How they look is left to the imagination.

With filters unhidden, the problem presented itself that I never really understood how filter feeding works, which is no wonder as I never looked it up. Many animals use it, from sharks and rays to bony fish and whales. So it works, but consider a whale shark or a basking shark as a gigantic sieve sweeping through the ocean. After a while, the filter will have sieved lots of food particles, now stuck against the sieve. The animal will have to scrape the food from it, not only to swallow it, but also to prevent the sieve becoming clogged. Remember that the gills are there as well, and you do not want to ruin respiration, not even for feeding. What bothered me is that whales might use their tongues to scrape clean their baleens, or so I supposed, but I was not aware of scrapers inside a whale shark's mouth.

Click to enlarge; Source: Brainerd, Nature 2001; 412: 387-388

Well, reading a few papers later I found out about something called 'cross flow filtration'. Naively, I had imagined the filter as a sieve at a right angle to the flow of water, allowing water to pass while particles get stuck. That's not how all filters work, though. The image above explains the process nicely. In 'cross flow filtration', the surface of the filter is parallel to the flow of water. Behind the filter there is a low pressure area, so water flows there. Apparently, particles move on parallel to the water, staying on one side of the filter, where they are  concentrated more and more. The papers then mention things like 'near the oesophagus', suggesting that the animal then merely has to swallow the concentrated particles and there you are. If you want to read more, I found a site where you can obtain a Nature paper for free here. Mind you, the fact that this was worthy of publishing in Nature in 2001 means that this is still all fairly new. The papers are somewhat vague on why the concentrated particles bunch up in a cul de sac waiting for the oesophagus to gulp them up, but I will accept this leap of faith; it cannot be easy to do an oesophagoscopy on a freely swimming whale shark.

So I sketched some more, filling in the inside of cloakfish contours, giving it a cross flow filter with a cul the sac leading to the oesophagus. Actually, since we are talking about a tetraradiate animal, there are four filters and four oesophagi leading to one stomach. I paint but am not a technical artist, so I needed some help with the perspective and also with visualising the insides of the cloakfish. I used Vue Infinite to provide me with as many perspectively correct views of the animal's inside as I wanted to help draw the cutaway.

Click to enlarge; copyright Gert van Dijk

What you see above are some aids in doing so. The holes help visualise the flow of water (but I must add that the gill design was changed afterwards). The painting, based on this design, is nearly finished, but I will not show it: there should be new material in The Book. My first look at the 'Demain' book showed a very large amount of previously unpublished animals, and that strengthened my resolve to keep much hidden. I must say that writing this post did remind me why I did it for a long time: it is fun; but time is short...                          

A better mantacloak animation

I'm not saying I will definitely resume blogging, but I may...

I had prepared some nice new animations for the Loncon3 speculative biology event, and decided to add a few scenes to make a nice animation. The thing is, rendering each image takes so long, that it becomes very difficult to tweak the result: whenever you think something like 'the cloakfish should come in here and not there', or 'the light should shine on it from there and not here', you have to reprogram a scene all over again, and then have to wait while the computer renders the 500 or so images for each short scene. So I do not think I will start a career animating Furahan wildlife documentaries. Just the odd scene every year or so. Mind you, I have some three new tetropter scenes as well. But I will wait a bit with those. I am thinking about the ultimate post on toes: 'why large running animals really need toes or toe-analogues so you should not give them elephantine feet'.

But first: A cloakfish accompanied by Debussy. This is NOT the best way to look at the video, as it is a 800x450 video. I will upload it on Youtube as well: http://youtu.be/IXaR5VxrMSA

More cloak and dagger stuff: cloakfish IV

Cloakfish have been discussed here previously; for the latest instalment, go here. Before I go on, I wonder how to call them; the plural of 'fish' is still 'fish' when you are talking about the same species, but as far as I know 'fishes' is correct when dealing with more than one species. So should I write sentences like 'Clown cloakfish are founds in their thousands under floatreefs' and 'The many cloakfishes of all shapes and sizes in the peri-Archipelago seas'?

Anyway, cloakfishes (!) were developed as animations before I painted them. So far, they were animated using MS-DOS, believe it or not, but the result was a bit two-dimensional. I later used Matlab too, but only as a painting aid, not to produce animations. Their bodies were very simplistic and the cloaks themselves were just sheets, without any thickness to them. But when I saw large cloakfishes in my mind's eye, they floated majestically into view, with cloaks as substantial as those of a manta ray. In fact, the one I will show now is a 'shortsleeved cloakfish' so it does look a lot like a ray, but with four-sided radial symmetry, obviously. So how could I realise such a vision?

Click to enlarge; copyright Gert van Dijk

Well, with difficulty... The overall strategy consists of several steps: the firsts relies on Matlab to design the overall shape of a cloak, as shown above. The various curves are combined to form the outline of the cloak as well as of the part of the body -the dagger-  it is attached to.

Click to enlarge; copyright Gert van Dijk

Then, flesh out the form by creating two surfaces for each cloak so it smooths into the dagger. What you see above are two such half cloaks, together making up one cloak. If you were to stick four such ensembles together you would have a full cloak and dagger assembly.

Of course, there is movement to think of, and the shape of the cloak has to be changed over its movement cycle. I divided the cycle into 200 steps to have some temporal resolution. For each stage of the movement there are eight half cloaks, so we are now at 1600 files. All these shapes are written to store as 3D obj files, again, using Matlab.

Click to enlarge; copyright Gert van Dijk

Meanwhile, design a head in a suitable program such as Sculptris. There you are; it is not very detailed, but more details would probably not be visible anyway. Also create an underwater landscape in Vue Infinite with a simple animation to allow the cloakfish to glide through the water. Open the programming language Python and write a script for Vue Infinite; from within Vue, use the Python script to load the eight appropriate half cloaks for each frame, the head too, assign textures, transport the lot to the correct positions, render an image and store it. At a reasonable resolution of 640x360 that will take about 30 hours.

Copyright Gert van Dijk

All that remains then is to create a film, perhaps add sounds, etc. What you see above is a trial version in which the cloakfish is just white. I rather like the movement. For a better view, visit Loncon3, where I intend to show a good version... 


PS 1: this is post #200...
PS 2: I am considering returning to blogging regularly after Loncon3.


(PS 3: this is to stop a particular site from copying my blog: 7InDB4PgQaCddePKQEqA )

The Creative Radiation of Cloakfish (Archives IX)

Cloakfish have not featured on this blog often (here and here); the last time was almost two years ago, so it is time to have another look, this time at their earliest evolution. Note that in the 'Archives' series of posts, 'evolution' often does not refer to the fictional biological evolution of these animals, but the evolution of the concept.

Click to enlarge; copyright Gert van Dijk

Leafing though the mouldy sketches in the damp crypts of the Museum of Furaha Biology reveals that their creative evolution started as an offshoot of Fishes. Furahan Fishes started their biological evolution not with series of paired limbs, but with an undulating membrane on either side of the body. Thinking about the movements of such membranes generated cloakfish as an offshoot. The sketch above was originally annotated in Dutch, but for this blog I overlaid them with an English translation. I hope they more or less speak for themselves. The  uppermost picture shows an undulating membrane with a central plane -a rectangle-. The second row shows the 'movement volume' of such an undulating membrane: over time, each point in this volume will be occupied by part of the membrane. In the third row I played with the idea of what would happen is this central plane would not be flat, but curved spirally itself. On the right side you can see how the membrane would undulate up and down around this central plane. The bottom row shows the movement volume of the membrane assuming such a curved central plane. The bottom right picture shows what would happen if you were to group three such volumes together, and that grouping is where Cloakfish depart from Fishes forever: we now have multiple membranes around a central axis, not one at each side of a body.

Click to enlarge; copyright Gert van Dijk

The next leaf of the sketchbook shows the evolutionary jump to a fully developed cloakfish:  the four membranes, the cloaks, surround a central rod, which I could not resist calling a 'dagger'. The body is largely a cylinder stabilised by four fins. The picture also shows an immediate variation on the theme: such a device can pull just as well as it can push. But the central plane of each membrane has reverted to a flat rectangle. I thought that undulation of the membrane around a curved surface would result in a net rotation force, so the poor animal would start rotating around its longitudinal axis. Perhaps I ought to consider the forces of that approach again, but at any rate that is how the basic cloakfish came into being.

Click to enlarge; copyright Gert van Dijk

Once there is a plan, it becomes tempting to start pulling at it to see where that leads to. The top animal here departs quite a bit from the general cloakfish, as its frontal cylinder is nowhere to be seen! It is in fact a tadpole with a cloak-and-dagger propulsion system (well, it also is not much like an earth tadpole in that it has no jaws and multiple eyes). The middle animal certainly is a generic cloakfish, although again with some twists: the front fins have rotated by 45 degrees compared to the cloak-and-dagger. The cloaks are much larger at their end than at the front or middle: this is probably as close as you can get to propulsion with a screw without continuous rotation. The bottom one has the fins and cloaks aligned, causing its four eyes to rotate as well. Whether bending the central rod as shown here would work well is dubious, is think.

Click to enlarge; copyright Gert van Dijk

Here is the result of more pushing the envelope. The left image shows a vertical cloakfish. I certainly did not spend enough attention on the cloak movement, as their shape looks rather unconvincing; then again, visualising the position of four membranes over time is not all that easy. The animal, looking suspiciously like a potted plant, could perhaps travel up and down as day makes way for night to filter plankton wherever it is most abundant. An animal with a horizontal position can do that as well, and if this animal is limited to the vertical position, that will limit its manoeuvrability severely, whereas a horizontal cloakfish could still choose to swim vertically upwards it is needs to; I like that idea. 

Click to enlarge; copyright Gert van Dijk

Of course, cloakfish can be flattened. That separates the cloaks so their movement volumes no longer all touch one another around the animal, but the membranes could still interact in pairs. How the membranes interact is explained on the main Furaha site (which is currently being redesigned). Note that this lineage has rotated its general body alignment by 45 degrees compared to the general pattern, so there no longer is a top fin, but there is a top eye. The dagger has increased in girth and now houses most of the body's internal organs; in conventional cloakfish this part of the dagger is hidden by the front cylinder.

Click to enlarge; copyright Gert van Dijk

Why not flatten the animal laterally? Here you see the result, this time with the overall rotation set to the 'top fin' mode. I doubt that such an animal, which probably has exquisite control over its cloaks, needs the four fins emanating from the front cylinder fro movement, but they do look good. The one on the right has also flattened the cylinder laterally, and is an overall exaggeration of the left one. I have this feeling that these are reef cloakfish.

Click to enlarge; copyright Gert van Dijk

Has the creative evolution of cloakfish stopped after this early burst of adaptive radiation? Not at all, but creative evolution is like biological evolution in that there may be periods of sudden intense speciation followed by slower adaptation. Dixon's recent mention of equipping his animals with a mother of pearl finish made me want to want to paint an animal with such a finish, and here is a first attempt. The result does not work well yet, but that is not surprising: painting a mother of pearl effect is difficult (if you want to see it done much better, search Google for 'Paul Quade Cambrian').

If I manage to reach that level I will certainly post the result here. Meanwhile, here is a  bioluminescent general cloakfish, another painting experiment.

Lifting the cloak on Cloakfish

There is an odd difference between drawings and photographs of animals. In a photograph a galloping animal may be caught in time in just such a way that only one of its legs touches the ground. No-one will think twice about whether this is 'correct' or not. But do the same in a painting, and people will start thinking that the painter has it all wrong. Something like that happened to my Furahan Fish IV, shown in this blog earlier.

Click to enlarge; copyright Gert van Dijk

Here it is again. I received some questions where it right front fin had gone. Was it amputated or had I forgotten it? No, I replied, I worked out the perspective and the missing fin is simply hidden by the body. I admit that I saw these people's point and have been tempted to tweak the perspective a bit and have the tip of the 'missing' fin emerge from behind the body. Its absence seems to be disturbing in a way. While working on Fish and Cloakfish I experimented a bit with the reasons.

Click to enlarge; copyright Gert van Dijk

This image shows two versions of a ray-like species of Fishes IV. The top image shows a layer for the perspective lines as well as a layer containing some rough idea of light and colour. Layers, for those of you not familiar with computer painting programs, are the computer equivalent of a pane of glass on which you paint. The painting as a whole can consist of many such panes, each consisting a different bit of the painting. The trick is that you can make layers invisible, change their transparency or swap their order. I use Painter 11 as I like its tools, that resemble artists' brushes more than the tools of Photoshop CS5. As you can see from the sketch the perspective effect is fairly strong, meaning that parallel lines diverge quite a bit. Still, the drawing seems to work, perhaps because all parts of the animal are visible.



Apart from 'regular' Fishes, I have been working on Cloakfish, completely unrelated to Fishes I to VI. You will find cloakfish on the main Furaha page, but also here on the blog. Apart from a few sketches almost all my earlier work on cloakfishes involved computer graphics, because I wished to see their four 'cloaks' move while swimming. At present it is time to paint them, but I wished to get their cloaks right, and doing that by hand would be very difficult. So I took recourse to computer graphics, a process best described as 'practical' ('cheating' comes to mind, but why not use tools when available?). To help the process, I adapted earlier programmes in Matlab so I could produce a cloak with any shape I wished, as on the left, that is warped to produce waves progressing along it, as on the right. Right; make four of them, export them as 3D files, import them in a suitable 3D program (Vue Infinite in my case, and we are ready to play.

Click to enlarge; copyright Gert van Dijk

Here is an example. The left panel shows the four cloaks, striped to help visualise their 3D shape, attached to a central axis (that is called a 'dagger', by the way). The body proper is formed by some basic shapes such as cylinders and rectangles. I thought it might be worthwhile to put lots of parallel rods in the image that could help get a better feel for the perspective. I set the focal distance of the imaginary camera in Vue to 35 mm, and that is the image in the left-hand panel. The perspective looks believable, does it not?

The right-hand side was produced in Painter 11. I imported the image from Vue and painted a rough cloakfish on a semitransparent layer above it. I decided to play around with the front edge of the funnel. In that stage of their evolution, cloakfish were all filter feeders, so the opening in the front doubles as a food and a respiratory intake. Some cloakfish evolved feelers, and those are what you see here. I wasn't happy with the sketch though, and wondered whether the perspective was part of the problem.

Click to enlarge; copyright Gert van Dijk

So I went back to Vue, altered the characteristics of the 'camera' to give it a long lens, and repeated the process. Well, well. The result looked more suitable for an illustration that the earlier one, even though that one was realistic. More realistic, because the combination of the lens with the size of the animal resulted in a perspective closer to what you would see if you were a human on Furaha. Obviously, my attempt at 'mathematical correctness' did not work. Perhaps it can be as counterproductive as its political counterpart. Anyway, I was not happy with the funnel opening.

Perhaps it was time for a redesign. Should cloakfish really all be filter feeders? There certainly are small filter feeders on Earth (polyps etc.), but there is curious gap in size in filter feeders: either they are small or they are colossal, such as whales. I cannot think of sardine- or tuna-sized filter feeders. While I haven't thought that problem through, it seems a real one. I wanted cloakfish to occupy lots of niches and needed a good range of sizes. Perhaps the beasts needed a separation of alimentary and breathing tracts after all.

Click to enlarge; copyright Gert van Dijk

Here is an all-new cloakfish. The inner body protrudes forward from the funnel, that, as before, contains the gills. I played with it having four jaws, but decided against it. What you see here is the latest thing in cloakfish design: a regular mouth with a horizontal split. It need not stay that way, though. As you can see, their eyes have shifted forwards on the funnel to improve frontal vision while still having excellent all-round vision. And the perspective? Well, a view without strongly convergent lines, such as this one, may help viewers get a good feeling for the animal's shape.

Furahan Fossils (bis)

Last time I wrote that I could not show an animation of a cloakfish, because it had been saved as a gif. Well, I could not resist to do one again. As I wanted to take advantage of a faster computer, I adapted the file to result in two cloakfish instead of one; a young? The male? I originally wished to change the relative sizes of body to tail in the small animal, so the body would exhibit 'allometric' growth, meaning some body parts of the young have a disproportionate size, such as large heads and large eyes in human children. That turned out to be trickier than I thought, so now the animal grows isometrically: infants are pure downscaled versions of the adults. I did however adapt the speed at which the smaller one moves its tail membranes, and its body movement now is less sedate as well due to less inertia. As a result, the animation definitely shows results of the difference in size between the two animals.

I also changed the phase differences of the four cloaks from the earlier one, so the animal is in fact using a different 'gait'. There is more of that on the website, to be found in the 'water' page, under 'swimming with membranes'.



The video above shows the result, but at a low resolution. Oddly, the width to height ratio is no longer correct (the image should be a bit wider). Perhaps I should have stuck to a 4x3 ratio instead of going for 720x480 pixels. I am not very familiar with all the various video formats. I did manage to add some titles though, and copied the idea for the soundtrack from an animation I showed earlier. I think I will put this animation up on the Furaha site; meanwhile, as an experiment, I also put it up on YouTube as an experiment. The image ratio turmed out better there...