OK well I did a whole day of test renders to figure out the threshold at which renders crap out at the end because of what we thought was a memory issue with GISD.
Windows never shows in the Performance Monitor that memory is being used up, so I am curious why that is. It feels more like a Terragen render buffer limitation.
I have determined 100% that the issue is related to having GISD turned on, but it's not merely a render resolution issue.
It seems to have more to do with how much highly detailed terrain is in the camera view (I am using 32k heightmaps/32,768 x 32,768 pixels).
I am not doing standard landscape renders pointing at the horizon with a sky and ground. I am rendering 100% ground from a top down view.
Basically what I did was create a simple scene not much different from the default scene, but I added a Heightfield Generate node to make a terrain instead of using my 32k Heightmap.
I will attach the scene here so you can try it out on a machine with enough CPU & RAM. I left the Heightfield Generate at 4096 so the scene will load faster, since auto generate is on.
The terrain I generated was 32km with 32768 points, so basically the same as a 1 meter DEM. You will need to up the heightfield generate to 32768 points to experience the hang at the end of the render.
I then did some 16k renders with GISD off to get a pretty fast 16k render on my 24-core Threadripper. My test scene renders in about 10 minutes.
I suspected that I could get a 16k render with GISD on to finish if I rendered just a small portion of the 32km terrain at 16k rather than the entire thing, and that hypothesis turned out to be right.
Then I rendered from a top down Perspective Camera with GISD turned on to see at what FOV would cause a render to hang.
Having too wide of a FOV on a highly detailed terrain (32,768 points/pixels) will capture an enormous amount of detail in the render.
I also tried a couple different resolutions in the Heightfield Generate node, and was able to get the full 32km terrain to render with GISD on.
So by reducing detail in the heightmap/heightfield it had a similar effect to reducing the FOV, and the render finished.
Incidentally, when I say the render wound hang at the end I mean it didn't finish. It didn't actually hang Terragen or cause a crash.
It just got to 99% and stopped, but appeared to still be working on something because the "Stop" button to abort the render was still there.
I was able to close the Render Frame Buffer window and continue working in Terragen.
I guess the bottom line is I don't really need GISD on for what I am doing. For anything high altitude you wouldn't see the details anyway. Correct?
Derek