[gdal-dev] Most optimal algorithm for contour correctness?

Martin Feuchtwanger feumar at shaw.ca
Fri Feb 15 17:04:45 PST 2013


I don't know about the gdal routines specifically, but:

 1. Re. dem/dtm generally, the most significant factor in interpolation
    results is the quantity (density, really) and quality of the source
    data, not the interpolation algorithm.
 2. Re. contours generally, they are cartographic artifacts, not
    geographic features and will never be more accurate than the source
    data (unless you know the data are very "noisy" and ought to be
 3. Re. segments vs splines, it depends whether the segment end-points
    are fixed and only their interiors are shifted, or the corners are
    shifted to make them rounded and the interiors fixed. The former is
    much better since the end-points are "primary" interpolations (based
    on data) and the interiors "secondary" (based on primary). Smoothing
    out the contours (either way) will make them cartographically
    pleasing, but the degree of "curviness" should depend on the assumed
    ruggedness of the original terrain (more rugged => less smoothing).

Hoping that helps and that others will comment on the specific gdal 

Martin Feuchtwanger  feumar at shaw.ca  604-254-0361

On 13/02/2013 7:15 PM, nav wrote:
> Am creating an app which correctly calculates contours from a DEM file or any
> height-map given to it. The correctness of the contour holding the most
> importance, since a person viewing the contours shouldn't end up taking
> wrong planning decisions and maybe losing their life by the route they
> choose after looking at the map.
> I have already tried using GDAL 1.7 source code, compiled it and added some
> features of my own to it for some other objective. Now I want to
> add-to/modify the source to be able to use the contour generation function
> of GDAL in C++.
> But before proceeding, I wanted to know:
> 1. If GDAL offers the best free contour generation algorithm available or is
> there any other library which I can link to my code and feed my DEM map to
> it and receive contour vector lines (or go thru research papers and
> implement the contour generation algorithm myself in C++)? If GDAL, then why
> is it the best?
> 2. A generated contour will basically be points connected with straight
> lines. Is it more correct for a contour to be depicted with connected
> straight lines or will it give a more correct result to use a spline to
> smoothen out the lines?
> I won't be interpolating any contours or the DEM because I've read on this
> website that interpolation leads to incorrect results.
> --
> View this message in context: http://osgeo-org.1560.n6.nabble.com/Most-optimal-algorithm-for-contour-correctness-tp5034148.html
> Sent from the GDAL - Dev mailing list archive at Nabble.com.
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