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I have a vector dataset of mean annual precipitation polylines, and I would like to generate a raster from them. I'm not sure the best way to go about it. ArcGIS has the Polyline to Raster tool but from reading its help file I get the impression it's not really designed to do what I need it to do. Obviously some kind of interpolation is required. I am hoping that SAGA-GIS might have a useful module. Either that or I guess I could convert the lines to points and then krige them.

I would appreciate learning from others' experiences on this one.

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3 Answers 3

Giving you GRASS and GDAL based answer if that's an option for you.

GRASS - r.surf.contour is the tool meant to interpolate contours to create DEM. http://grass.osgeo.org/wiki/Contour_lines_to_DEM#r.surf.contour

If using GDAL is an option, try this. ( Install OSGeo4W and run following from shell ). This is an easier option, but kind of a hack, so use with care.

Assuming your isolines layer is called isoline.shp and your polylines have an attribute named PRECIPITATION

Convert to raster , X is the resolution of the output raster

gdal_rasterize -a PRECIPITATION isoline.shp iso_raster.tif -tr X X

Fill intermediate values by interpolation, change XX to appropriate value.

gdal_fillnodata.py -md XX iso_raster.tif iso_raster_interpolated.tif -mask iso_raster.tif

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You called this a 'hack' . What is the problem with this? Is the final output not correct? –  Devdatta Tengshe Oct 17 '12 at 5:33
    
I used that term because gdal_fillnodata.py wasn't designed for this purpose. I believe the output would be correct but you need to choose the correct value of the -md based on trial and error. –  spatialthoughts Oct 19 '12 at 4:59

If you have the Spatial Analyst extension you could try the Topo to Raster tool. This tool is primarily used for converting existing elevation contours to a hydrologically correct DEM but it could work fine for your purpose since it bascally uses some modified interpolation functions.

ESRI: This method "Topo to Raster" uses an iterative finite difference interpolation technique. It is optimized to have the computational efficiency of local interpolation methods, such as inverse distance weighted (IDW) interpolation, without losing the surface continuity of global interpolation methods, such as Kriging and Spline. It is essentially a discretized thin plate spline technique (Wahba, 1990) for which the roughness penalty has been modified to allow the fitted DEM to follow abrupt changes in terrain, such as streams and ridges.

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Use the topo lines to create a TIN where the TINs z values are the precip values from the contours, convert the TIN to a raster.

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Than you for answering--but isn't this much already stated in the question? I believe the OP would like to know how to do these things. –  whuber Jul 21 '12 at 16:36

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