In article <397F27BE.5847C69C@psu.edu>, Paul Jones <pdj### [at] psuedu> 
wrote:

> I would like to place something on the surface of a height field, how
> would I do this?

The easiest and most robust way to do this is to use the trace() 
function in MegaPOV. This function allows you to find the intersection 
of a ray with an object...just trace a ray straight down at the height 
field from above the point where you want to place an object, and you 
can get the exact position as well as the surface normal("up" direction) 
at that point.
There is also a hf_height_at keyword, but this is not as useful: it 
doesn't give the normal, and it only works with height fields.


> Specifically I would like to model the Great Wall of China, any 
> thoughts? Any good tutorials or sample scene files I could peruse?

This sounds interesting...you might try creating a spline {} with the 
points from trace(), and have the wall follow that, instead of having it 
directly follow the surface of the ground. Or you might be able to do it 
with an isosurface...that might be faster rendering, and can give good 
results.
There is at least one stone wall macro in povray.binaries.scene-files, 
you might want to have a look at that for ideas. I'm sure there are 
other stone/brick macros out there.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

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