[GRASS-user] TIN and B/T correction in grass...

[Luca Penasa]

>From IDRISI manual:

"Contour lines at the top of a hill are shown in Figure 11-4a. In Figure
11-4b, the highest contour is shown along with the
resulting triangles created within it when a constrained TIN is
generated. Because all three of the points for all the trian-
gles have the same elevation, the top of the hill is perfectly flat in
the TIN model. Our experience with actual terrain tells
us that the true surface is probably not flat, but rather rises above
the TIN facets. The edges of the TIN facets that lie
below the true surface in this case are examples of what are called
“tunnel edges”. These are identified in Figure 11-4b. A
tunnel edge is any triangle edge that lies below the true surface.
Similarly, if the contours of Figure 11-4a represented a
valley bottom or depression, the TIN facets of 10-4b would describe a
flat surface that is higher than the true surface. The
edges of the TIN facets that lie above the true surface would then be
termed “bridge edges”.
Bridge and tunnel (B/T) edges are not restricted to hill tops and
depression bottoms. They can also occur along slopes,
particularly where iso-lines are undulating, and along ridges or
channels. Two such examples are shown in Figure 11-5.
To optimize a TIN, B/T edges may be removed. B/T edge removal could
technically be performed on an unconstrained
TIN, but this is not recommended and is not allowed in IDRISI. An
optimal TIN will be generated if iso-lines are used as
the original input for TIN generation, the constrained triangulation is
used, and B/T edges are removed.
While many of the concepts of this section are illustrated with
elevation data, the procedures are not limited to such data."




Il giorno mer, 29/10/2008 alle 22.25 -0700, Hamish ha scritto:
> Luca Penasa wrote:
> > Is there a way for apply a bridge/tunnel TIN correction in GRASS?
> > Is there any other similar TIN correction yet implemented in GRASS GIS?
> > Anybody know if this function is only implemented in IDRISI?
> 
> 
> can you explain what this function does exactly?
> 
> 
> no idea,
> Hamish
> 
> 
> 
>       
> 

 
 
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