How to convert many polygons to a bitmap

Question

How to take a set of polygons that contain arbitrary values, and create a corresponding bitmap image, where each pixel contains a polygon value in this place?

To put the question in context, my polygons contain information about the average number of people per square kilometer in the polygon. I need to create a bitmap / bitmap that contains pixels representing the population in 200 meter boxes.

In the past, I did something similar when I used a polygon to create a mask, drawing in raster and fill values, and then converting the bitmap into an array that I can manipulate. I am sure there is a better way to do this!

I clarify the question a little on request.

• There are several polygons, each polygon is a set of vectors
• Each polygon will have a unique value.
• Polygons do not overlap

thank

Nick

Answer 1

@Nick R

I originally used ArcGIS 9.2, but this does not work with C # and 64-bit, so I now use GDAL ( http://www.gdal.org ).

Does gdal_rasterize not do exactly what you want?

Answer 2

What GIS software do you use? ArcGIS offers the Polygon to Raster tool in ArcGIS 9.2 or later, which is scriptable as a function of PolygonToRaster_conversion.

PolygonToRaster_conversion (in_features, value_field, out_raster_dataset, cell_assignment, priority_field, cellsize)

Answer 3

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-Adam

Answer 4

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 have a NY * 2 array of x positions: int x[NY][2]
foreach polygon
  clear the array to -1
  for each edge line
    foreach horizontal raster line iy intersecting the line
      generate ix, the x position where the raster intersects the line
      if x[iy][0] == -1, set it to ix, else set x[iy][1] to ix
    end foreach iy
  end foreach edge
  foreach iy
    fill the pixels between x[iy][0] and x[iy][1] with the polygons label
  end foreach iy
end foreach polygon

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If the polygons are NOT convex, this is a little different. Wherever the edge crosses the raster line, switch all the pixels from there to some randomly chosen X coordinate, such as the left edge of the “screen”. When you finish all the edges, only the internal pixels will switch an odd number of times.

Answer 5

ImageMagick can convert from svg to png, maybe you can take a look at the code or just create svg and use IM to convert? Scruffy does it.