Re: [Gdal-dev] Algorithm Development

Lucena, Ivan ivan.lucena at pmldnet.com
Tue Sep 9 00:08:35 EDT 2008

```Frank, Fodder,

There is a nice open source implementation of interpolation on TerraLib.org [1] that takes any vector and produces a raster based on nearest neighbor, average nearest neighbor, distance weigh average nearest neighbor, box interpolation and average box interpolation.

Best regards,

Ivan

[1] http://terralib.org/html/v320/html/class_te_interpolation_algorithms.html

>  -------Original Message-------
>  From: Frank Warmerdam <warmerdam at pobox.com>
>  Subject: Re: [Gdal-dev] Algorithm Development
>  Sent: Sep 09 '08 03:22
>
>  Fodder wrote:
>  >
>  >
>  > Frank Warmerdam-2 wrote:
>  >>
>  >> - An algorithm for interpolation in regions of a raster.
>  >>
>  >>
>  >
>  > Hi Frank,
>  >
>  > Happy to hear about your research. I'm interested in the interpolation in
>  > regions of a raster algorithm. In particular:
>  > - What interpolation methods with be supported?
>
>  Fodder,
>
>  A simple "four quadrant inverse distance" interpolation is used.  That is,
>  I find the closest valid pixel for each of the four quadrants and then
>  mix them based on inverse distance weighting.
>
>  Then I apply some number of 3x3 average filtering in the interpolated areas
>  to smooth out various artifacts somewhat.
>
>  While this approach has a number of problems, I feel it is suitable for
>  use in a variety of circumstances, including sparse data (such as might
>  be the result of burning a bunch of known sample points into a raster),
>  holes in data (such as SRTM or interferometry DEM holes), or to interpolate
>  in data after burning contours into a raster.
>
>  This is in contrast to approaches such as the spline interpolation in
>  GRASS which produces (presumably) superior results when interpolating in
>  modest sized holes in rasters but that does not scale well to sparse data
>  or to large empty regions like with contours.
>
>  > - What vector sources will be supported (if any) (points only, or polyline
>  > polygon etc)?
>
>  The fill algorithm does not directly use vector data.  If you want to produce
>  raster data by interpolating from vectors you would need to first use
>  gdal_rasterize to turn the vectors into a raster, and then use the fill
>  program/functions to interpolate in the holes.  I believe someone
>  (Andrey? Even?) has been improving gdal_rasterize to support additional
>  data types.
>
>  > - Will it be incorporated in Gdal_Grid?
>
>  No.  I'm only moderately familiar with gdal_grid but my understanding
>  is that it does not scale particularly well to handling huge numbers of
>  points to interpolate from.  But generally speaking gdal_grid will still
>  be much superior for interpolating reasonable amounts of point data
>  to build a raster.
>
>  > - When you say regions, do you mean vector polygons or raster zones?
>
>  Raster zones.
>
>  Note that this algorithm is already in trunk as the function
>  GDALFillNodata().  However, I've had some problems with the post
>  fill smoothing filtering and haven't really finished cleaning things
>  up and documenting them.
>
>  Best regards,
>  --
>  ---------------------------------------+--------------------------------------
>  I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
>  light and sound - activate the windows | http://pobox.com/~warmerdam
>  and watch the world go round - Rush    | Geospatial Programmer for Rent
>
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```