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POConverting vector-contoured regions (borders) to a raster map (pixel grid)
 

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  1. POConverting vector-contoured regions (borders) to a raster map (pixel grid)
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    <p>I have a map that is cut up into a number of regions by borders (contours) like countries on a world map. Each region has a certain surface-cover class <em>S</em> (e.g. 0 for water, 0.03 for grass...). The borders are defined by:</p> <ul> <li>what value of <em>S</em> is on either side of it (0.03 on one side, 0.0 on the other, in the example below)</li> <li>how many points the border is made of (<em>n</em>=7 in example below), and </li> <li><em>n</em> coordinate pairs (<em>x</em>, <em>y</em>). </li> </ul> <p>This is one example. </p> <pre><code>0.0300 0.0000 7 2660607.5 6332685.5 2660565.0 6332690.5 2660541.5 6332794.5 2660621.7 6332860.5 2660673.8 6332770.5 2660669.0 6332709.5 2660607.5 6332685.5 </code></pre> <p>I want to make a raster map in which each pixel has the value of <em>S</em> corresponding to the region in which the center of the pixel falls. </p> <p>Note that the borders represent <em>step</em> changes in <em>S</em>. The various values of <em>S</em> represent discrete classes (e.g. grass or water), and are not values that can be averaged (i.e. no wet grass!). </p> <p>Also note that not all borders are closed loops like the example above. This is a bit like country borders: e.g. the US-Canada border isn't a closed loop, but rather a line joining up at each end with two other borders: the Canada-ocean and the US-ocean "borders". (Closed-loop borders <a href="http://en.wikipedia.org/wiki/Lesotho" rel="nofollow noreferrer">do exist</a> nevertheless!)</p> <p>Can anyone point me to an algorithm that can do this? I don't want to reinvent the wheel! </p>
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    1. USJean-François Corbett
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