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I have a shapefile with 2M measurement points (each measurement point has a resolution of a 1/10). How can I aggregate points around each other if and create polygons out of it?

They do not have to match a grid, polygons should not overlap. In addition, I would like to reduce the resolution, e.g. aggregate all points around a 1/2 resolution.

Can I do this with QGIS or in PostGIS?

I have tried convex hull, but it seems that the polygons overlapped. Also, some answers are referring to ArcGIS 10, which I do not have.

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how about creating a Voronoi diagram which can then be dissolved? –  underdark Apr 14 '13 at 14:21
    
How can I adjust the resolution with the Voronoi diagrams? –  neurix Apr 14 '13 at 16:05
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The only way this problem makes sense to me is if the measurement value is related to the position such that points near each other tend to have similar/related values. (If the point value is unrelated to position, then I see no hope in aggregating them into polygons). If my interpretation is correct, why not just use a contour finding routine as if the data were a DEM or something similar? Generate iso-value lines at multiples of .5 and create the corresponding polygons. –  Llaves Apr 14 '13 at 16:23
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Without using a grid, it's going to be quite hard to avoid overlaps without using a Voronoi approach. You can ST_Collect them and then pass them to ST_ConcaveHull if you have a recent PostGIS. That will produce a result close to what you want, but without a "no overlap" guarantee.

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