[Gdal-dev] Digital Elevation to Vector Conversion

[Frank Warmerdam]

Joshua Lamorie wrote:
> Gidday there,
>  
>     I have an application that requires elevation data in some form of 
> vector format.  I'm not a GIS guy, so please excuse my use of 
> vocabulary.  I need a vector form of 'iso-elevations', similar to what 
> appears on topographic maps.
>  
>     I currently have DTED and DEM data for the target areas, but I would 
> like to get the same data in a vector format.  Is it easy to convert?  
> I've started sketching out some routines for this, but my net search 
> didn't really bring up much.  It seems I might be able to buy some 
> software that will do it, but I really would like source, or an API.
>  
>     I've written my own DTED library, but I might switch to GDAL if my 
> evaluations work out (since I don't want to write my own DEM library).
>  
>     Any advice to a neophyte?

Joshua,

The gdal_contour utility program (available in GDAL 1.2.0) should do a good
job of generating elevation contour lines (iso-elevations) from a single
elevation file in any GDAL supported raster format (including DTED, USGS DEM,
and several more).  The downside to the gdal_contour program is that it
produces very dense contours.  Basically, there will be a line segment on the
contour for each elevation "pixel" crossed.

If you find you really need the contours "generalized" (reduce the number of
vertices along the contour but preserving most of the information content)
then you will need some additional utility.  I don't have anything that does
that.  A number of "mainline" GIS packages may have good capabilities for
generalizing while avoiding any crossing or touching of the generalized
contour lines.  However, this is not a trivial task.  So if it is critical for
the generalized contours to be non-intersecting you would want to ask very
carefully about the capability of any software you purchase.

If you don't require generialization of the contours, or if isn't critical
that they be non-intersecting in all cases then you could just use the GDAL
utility, and do any required generalization via a number of simple common
methods - even just dropping some percentage of points along the contour.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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