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Why
About Truespace Archives
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Why // Archive: Tech Forum
Post by rjeff // Feb 10, 2008, 3:26pm
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rjeff
Total Posts: 1260
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Yes I am full of questions tonight...but this is something that has been bothering me. You see the image. Why does the sphere reflect the image properly, but the plane does not? It seems any flat surface distorts the image. Any body got a clue. |
Post by Burnart // Feb 10, 2008, 4:04pm
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Burnart
Total Posts: 839
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How have you done it?
It looks like the environment image used for the reflection is mapped across a virtual sphere or hemisphere so the flat surface is picking up a only small section (ie. where its pointed) whereas the sphere is getting it all. You would need a really high resolution in your environment image to get around it as far as I can tell. |
Post by hultek43 // Feb 10, 2008, 4:06pm
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hultek43
Total Posts: 234
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Have you tried quad dividing the plane a few times? |
Post by Jack Edwards // Feb 10, 2008, 4:18pm
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Jack Edwards
Total Posts: 4062
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Hmm, I think I remember seeing something like this posted before. Which render engine are you using? |
Post by rjeff // Feb 10, 2008, 4:26pm
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rjeff
Total Posts: 1260
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lw..using GI with a HDRI image. |
Post by kena // Feb 10, 2008, 4:41pm
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kena
Total Posts: 2321
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Try applying a Plainer UV map to the plane. When You first create it, I think that it's UV is set to whatever the default is. therefore, it only reflects a small portion of your HDRI and magnifies it. |
Post by rjeff // Feb 11, 2008, 6:42pm
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rjeff
Total Posts: 1260
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nope...applied planar and no go..still distorts it. |
Post by kena // Feb 11, 2008, 7:33pm
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kena
Total Posts: 2321
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would you be willing to post this little scene? I can tell that the plane is zooming in on just the bottom of what looks like the bridge struts, but maybe if we all work together we can find out why. |
Post by Shike // Feb 11, 2008, 11:03pm
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Shike
Total Posts: 511
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Burnart is on the right track I think.
I've seen this in several renderengines and I think you would get the same result in real life. ( if you were photographing a flat mirror inside a sphere with a low resolution texture on it..;) )
The only difference between render engines might be blurring or filtering of the image. Try blurring the environment image to get a less blocky reflection in the flat surface. Might look more like DOF.
Also, compare this effect in a perspective render and a non-perspective. The non-perspective one reflects an even smaller area of the enviro.
EDIT:
Hmm, quick test with sphere, rounded cube and flat plane showed I'm wrong here.
The flat surface on the rounded cube should reflect the same as the plane, but the plane acts like a magnifier. Strange. |
Post by Shike // Feb 11, 2008, 11:56pm
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Shike
Total Posts: 511
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Come to think about it, I also kinda remember a topic about this..
11019
..probably in the bugs section?
The flat surface on the rounded cube shows what it should look like. Reflection looks larger since it reflects a smaller area of enviro.
The parallell flat single surface should give the same result but doesn't. (an non-rounded cube also give bad reflection) :confused:
(similar results in Lightworks and VRay)
UV-mapping and Subdivision doesn't affect it. Copying the rounded cube and deleting everything except the flat front surface didn't help. |
Post by Dirk_Fist // Feb 12, 2008, 6:00am
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Dirk_Fist
Total Posts: 15
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My guess is the "Flat" plane and the "flat" cube has a single normal per face,
where the "rounded" cube has normals at each vertex.
And the renderer uses a different method for "flat" faces as opposed to "rounded" ones. |
Post by Shike // Feb 12, 2008, 6:53am
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Shike
Total Posts: 511
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Ah, you got me thinking here....
Going back to claim that the first assumption was correct.
The flat surface reflection is correct. It should look like it does, and higher resolution on the enviro is the solution.
11024
In the example above(with house_outside_pano_half_VC.hdr):
Left cube: Uses faceted shading. (compare the reflected brush with the background, size looks correct)
Right cube: Uses autofacet or smooth. (shrinks the reflection, like a slightly spherical surface)
Soo...it seems like the rounded cube has the incorrect reflection? More normals due to autofacet...?
( Actually very clear when placing an object in front, perfect reflection in the left cube, bent and shrunk in the right one.) |
Post by kena // Feb 12, 2008, 9:12am
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kena
Total Posts: 2321
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I'm at work now.. anyone want to test to see what happens if you apply a spherical UV map to a plain? |
Post by Shike // Feb 13, 2008, 3:02am
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Shike
Total Posts: 511
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I'm at work now.. anyone want to test to see what happens if you apply a spherical UV map to a plain?
UV-mapping doesn't affect raytraced reflections. (tested it: the leftmost plane below has spherical UV)
11034
Objects in Image above from left,
Plane
Rounded cube with faceted shading
Rounded cube with autofaceted shading
Sphere with autofaceted.
Ok... Burnart had the correct answer for Rjeff,
then I got sidetracked by the behavior of my rounded cube
which in turn Dirk_Fist had an answer for. :) |
Post by Georg // Feb 13, 2008, 3:12am
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Georg
Total Posts: 270
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Thanks Shike, very instructive!
Something to remember when you don't want reflections to be perfect.
Georg |
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