AO Mapping splays upwards?

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  02 February 2013
AO Mapping splays upwards?

Hey all,


Just a question. Is it normal for Ambient Occulsion maps to flow upwards? Is there a way to adjust this?

Shouldnt they be neutral or downwards? I would think downwards, if anything, would be a natural shadow flow direction, but upwards seems odd to me.

I am creating AO's with Max 2012, Mental Ray, no lights of any sort.

NOTE: You cannot really see in that screenshot what I am talking about. The shading or shadow from the elevators flow upwards on the side of the rudder area. Likewise on the wing struts up the sides of the doors.


Many thanks.
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  02 February 2013
AO has absolutely nothing to do with light or shadows, it's just a vizualisation of how much a point on a surface is occluded by the surrounding surfaces.

So yes, it's normal(because it is correct).
If you want to elimate shadings on surfaces pointing upwarsds you either need to set a light or render a normals pass to, multiply that with the color for surfaces that point up and use the result as a mask for an AO pass(it's a wee bit of compositing).
 
  02 February 2013
Or composite shader material with AO and add falloff with Towards/Away and worldZ-axis
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  02 February 2013
You could always bake it using the old skylight and lighttracer method. That bakes it from a sky hemi-sphere so it is more directional. You might get a better result for what you want.

At least that's how I remember it. It's been ages since I used it.
 
  02 February 2013
Originally Posted by stefan: Or composite shader material with AO and add falloff with Towards/Away and worldZ-axis


I'll check that right now. Thanks Stefan.


Originally Posted by robinb: You could always bake it using the old skylight and lighttracer method. That bakes it from a sky hemi-sphere so it is more directional. You might get a better result for what you want.

At least that's how I remember it. It's been ages since I used it.



Thanks Rob. I know nothing about LightTracer, only Mental Ray and ScanLine. I'll check this out. I have only been able to get good results with Mental Ray using Material Override with the MR AO Material. Its finally getting to be what I want. But I would like the shading to splay downwards if anything, or neutral.


Many thanks, gentlemen.


Bill
 
  02 February 2013
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