View Full Version : HV Incidence Angle weirdness?

03-23-2006, 05:58 AM
I am doing a scene (LW 8.5) of a fly-by of a small island covered with HV vegetation. The camera points to a target on the island, the single Distant light is fixed. As the angle between the light and the camera changes, the HV vegetation lightens and darkens strangely, like the angle change is affecting the diffuse or specularity (or something else.)

I'm attaching some stills to show the problem, I can zip up the scene if anyone wants to see it, and here's a link to the animation (warning: 30 MB): http://www.electricgearbox.com/images/hv_island1.mov

Does anyone have any idea what's causing this strange effect, and more to the point, how to fix it?????

Thanks in advance....

03-23-2006, 03:03 PM
I checked out the movie. It almost looks like you have a light with fall off moving with the camera-- very wierd.

I would probably try to experiment with other settings instead of incidence angle, since, even if you get the vegetation-going-dark problem fixed, the shading will still change across the surface as the camera changes position-- specifically the lightest areas of the contours will always be perdendicular (or parallel) to the camera, depending on the orientation of the gradient. It may look more natural to just use 'previous layer' and let the scene key-light (sun) create the shading on the surface via shadows from the contours.

Also for troubleshooting the scene, you could try to add some lights above the island, and in the HV panel-- I think it's under shading, check the use all lights box. See if it still darkens during your camera move.

Hope this helps.

03-23-2006, 10:31 PM
I think he's right about using different lights, the problem may be partially that you have one single light source, which is unrealistic. Light coming from one singular direction will give you very clear lines of falloff, which you don't want. What the scene is missing as far as realism is ambient light - light being bounced and diffused by the sky, clouds and other objects.

Other guesses I have would be to try turning off specularity. It has a steeper, more noticeable falloff than just diffuse, or you could reduce the gloss to a very small amount.

It also seems to be acting like hair - like it's all streched in the same direction and gives off a kind of anisotropic look - do you have a stretch direction set on the hypervoxels?

03-24-2006, 06:16 AM
I've tried playing with the lights, the scene, and the HV settings and eventually I found that the Smoothness setting of the HVs would affect it. Nothing else seemed to matter. I don't have an alignment or stretch set on the particles, and there's only one light in the whole scene now - a Distant light pointing straight down.

Maybe someone from Newtek will chime in and say "Oh yeah, that's the so-and-so problem, you can get around it by doing X."

03-27-2006, 10:29 PM
Nice sequence. I was wondering if you are using a distant light like the default one in Layout or a distant light generated by Sky Tracer? Perhaps if it is a skytracer light your lighting problem is related to skytracer sun being blocked by a moving cloud. I think that is a feature in Skytracer but I am not positive. The reason I say this might be a problem was because I did an animation that had timelapse skygen or something and I got weird shadows, but I wasn't using HV. But it appears that you figured it out with the HV smoothness settings. Good Luck.