Wibbly-wobbly spacey-wacey

A few weeks ago I posted some first tests of displaying isosurfaces in Blender. This got interrupted by the receipt of a referee report, so now back to the wibbly-wobbly spacey-wacey stuff.

I used to poo-pooh isosurfaces as being inherently inferior to volumetric renders because they lose information. They also feel somewhat like cheating, because rendering a surface is easier and uses a lot less memory. While all this is true, I'm somewhat reconciled to their uses : isosurfaces depend far less strongly on viewing angle than volumetric renders. That makes them much easier to highlight features in an objective way, and contrary to my intuition, this can make them better for finding faint structures rather than worse. The eye tends to get very confused when you have really bright and faint sources together, but slap on a fixed level surface and BAM you can see if what you're looking at is significant or not. You might still miss the very faintest stuff, but there can be a surprising amount to see at relatively bright levels.

The other nice thing about isosurfaces is that because they're very fast to generate (typically seconds per surface in these examples, if not less), they're easy to animate. Last time I showed some fixed-level turntable animations. Here's M33 from the AGES HI survey shown at a variable flux level, starting with the brightest gas and ending with the faintest. Each frame decreases the flux to 97% of the previous value.

There's a whole bunch of clouds around M33, most of which show up quite well in the animation. It's not as good as manually tweaking the level of each region, but it basically works. I probably should have frozen the final level and rendered a full rotation, but never mind.

Here's the same sort of animation but using NGC 4361 from the WSRT HALOGAS survey, which also has a bunch of weird stuff going on around it :

And finally, here's a test of a true time series from a simulation. This is an old one from when I was trying to learn the FLASH hydrocode and my galaxy got all unstable because of a bug in the boundary conditions. Four fixed levels all animated, showing how the nice stable galaxy gradually goes fully wibbly-wobbly and eventually gives up. Does it help analyse what went wrong ? Not really, but it looks nice.