[GRASSLIST:9211] Re: Raster DEM creation suggestions

[Ian MacMillan]

Maciek, I was just implying that if you have several different file 
types (multiple point, line, and raster files), then you would have to 
interpolate each separately, then patch them together.

-Ian

On Nov 23, 2005, at 12:32 PM, Maciek Sieczka wrote:

> 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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>
 >
 >
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