[GRASS5] TINs as 3D vectors

Radim Blazek blazek at itc.it
Tue Apr 19 09:48:58 EDT 2005

Pieter Bos wrote:
> What do you mean exactly with contours? The outer boundary of the TIN is
> very easy to generate, just output all boundaries of a TIN that only
> have one triangle adjacent to them, instead of two. We have something
> that can add a different category value to different 'objects' (objects
> consist of connected triangles) automatically as well. 
> We also have used the GNU triangulated surface
> library(http://gts.sourceforge.net/, yes that does have a compatible
> license) to calculate intersection lines between two TIN's, which are
> lines where the TIN's have the same x,y and z-value. (we compute the
> union, intersection and difference of vague objects with them - although
> those are defined for vague objects and might probably not be of general
> use). You could probably modify it to calculate contour lines with that
> as well by intersecting with some horizontal surfaces, if you would want
> to, although I'm sure a better approach is possible.

I mean the lines with the same height, the same as produced by r.contour 
but from TIN. Cutting by a surface will be slow, it is easy to do it 
directly, just to calculate 2 points with the same height in a triangle 
and write out the line.

> There is 2D visualization though, which currently maps z values between
> 0.0 and 1.0 to a gray value. Can be changed to accept any range of
> z-values, if needed. Supports showing several TIN's(vectormaps..) at
> once, using transparency and different colors to distinguish the
> different TIN's. However, you'd need a new front-end to call this
> visualization, it now works by reading the names of several vectormaps
> stored in a database and only works with the limited z-value range. Not
> much work to do, if required... Would be of any use?

The visualization should be integrated into a standard viewer, I think.


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