[GRASSLIST:9210] Re: Raster DEM creation suggestions

[Maciek Sieczka]

On śro, 2005-11-23 at 10:07 -0800, Ian MacMillan wrote:
> Without seeing your data, as a general rule, use v.surf.rst to convert 
> vector data (points and lines) to a raster surface.  Then you can use 
> r.patch to patch all of your data into a single file.  You can use 
> something like r.surf.idw or r.fillnulls to fill in spaces from there.

Ian, I'm not sure if I understand what you mean - do you suggest to
interpolate with v.surf.rst in several separate, adjacent regions and
to mosaick the pieces after that? Why so? Is there a reason it would be
better than doing the whole interpolation in one step?

> When doing all of these steps make sure that your region resolution and 
> bounding area is set appropriately.  This will affect both processing 
> time and quality of data.  Depending on the size of your datasets, the 
> interpolations may take a very long time (hours to days for large 
> datasets).  Test your method first on a small piece of your data by 
> reducing your region size (but keep the resolution the same as you want 
> for your final product).
> 
> Hope this helps get you started.
> -Ian
> 
> 
> On Nov 23, 2005, at 5:53 AM, Travis Kirstine GIS Tech wrote:
> 
> > Hi all,
> > I'm fairly new to the grass world, and am hoping someone could provide
> > assistance regarding DEM creation.  I have elevation data in several
> > formats: orginal points

If your elevation points are distributed in a uniform way (not
clusterized) and dense enough compared to to desired DEM resolution,
v.surf.rst is the best way to go.

>  and breaklines created during ortho rectification in dgn format

Bad news, no support for breaklines in Grass interpolation modules.
Neither for soft-breaklines (that would require TIN support), nor for 3d
hard-breaklines. Elevation disctontinuity lines are not supported
either. Hopefully one day, somebody.


> > ESRI TINS created from dgn

If you are happy with your TIN quality you can try converting it to a
grid in Saga GIS (FOSS, for Linux and Windows, use the latest 2.0 beta)
and import this intogrid  Grass. No direct support for TIN in Grass.

> > file and 1m contours in shapefile

If your contour lines are not evenly distributed and there are rapid
gradient changes in elevations (eg. gullies, walls, land slides) you
will have a hard time trying to interpolate it in Grass. The more
troubles the finer resolution you need of course.

BTW, is there anybody able and willing to add natural neighbour
interpolator to Grass 6.1? I recall there was v.geom in 5.0 (or 4.x?),
wasn't it a natural neighbor interpolator?

Maciek


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