Great explanation. Thanks very much. I will try my image map again.
Best,
Dennis

"Gilles Tran" <tra### [at] inapginrafr> wrote in message
news:3ecd14ce$1@news.povray.org...

> 3eccfd86$1@news.povray.org...
> > This is a beautiful effect. Can someone tell me how the slope feature is
> > working to create this? (I'll take the answer in Newusers if necessary).
>
> Note: I didn't invent this technique, Kari Kivisalo did.
> Slope at a given point uses the angle between the direction value and the
> normal on the surface at that point In this case the direction value is
the
> camera_location->look_at vector. Points looking at the camera get a black
> texture and points looking perpendicular at the camera (the ones on the
> surface edge) get a blue one.
> In fact the code I posted should be rewritten as follows to be more
> consistent with the docs :
>     texture {pigment {slope {cam_lookat-cam_location,0,0.6}
>             color_map{[0 rgb 0][1 rgb z*2]}}
>             finish {ambient 1}
>     }
>
> It's not a "true" aoi effect because a real one should use (I suppose) the
> normal/camera->surface_point angle, not the normal/camera->look_at angle,
> but the approximation works for artistic purpose. I could be mistaken
> though.
>
> > Also, slope doesn't seem to work with image_maps...
>
> Hmm, slope works fine with image_maps. I guess that your problem is trying
> to use a map_type 0 map on a very concave/convex object... map_type 0
image
> maps only works well on relatively flat objects (such as terrains),
whatever
> the pattern. On other objects, the map needs to be a non-planar uv_map
> (map_type 1 on a sphere etc., or uv_mapping) to get proper results.
> In fact my most common use for the technique is to create for poser models
> skin maps (uv) finishes having higher diffuse values at shallow angles.
>
> > Are there other
> > limitations to its use with various types of pigments or would that be
the
> > main one?
>
> The main limitation is that it doesn't work with turbulence. A workaround
> for this consists in putting slight variations of the slope map within a
> pigment map controlled by a pigment pattern :
> pigment{pigment_pattern{agate...}pigment_map{[0 slope...][0.5 slope...][1
> slope...]}}
>
> Slope isn't a easy pattern to figure out though.
>
> G.
>
>
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>
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