From OpenStreetMap Wiki
Improving Contour Rendering
As is visible from the first rendering, GnuPlot can produce some pretty weird contours. Below are some suggestion on how to improve this, add any more that you can think of.
- Join contour segments at overlaped nodes.
- Smooth contour ways after GnuPlot computes them? Bit of a head-ache, but possible.
- GnuPlot's dgrid3d does a poor job when there is little data at the edge of the map. The contours are filled with a reducing value, which looks rather weird to say the least. It looks like the best (only?) way to solve this would be to pre-process the data into a 2D matrix of distance values, but I'm not quite sure what the algorythm for filling the 'outside' of the matrix would be.
Features to Add
- Output data as a native OSM file with 'distance=xx' tags.
- Allow GnuPlot to read navtive OSM file.
- Read target position from stdin in 'lat,long' or OSM format
- Process more than one target, output nodes with the distance to the closest 'target'