0

I've got a huge database of depth points for the whole Irish sea which I'd like to be a nice smooth surface, or at least have a depth value associated with the entire area (i.e. include the inter-point spaces). I've tried interpolation but can't get it to work well, so I thought to make Voronoi polygons from the points, and then graduated colour them.

Problem: In 2.1 master, a blank column is created in the Voronoi polygons shapefile, and switching from single symbol: single symbol towards graduated results in a complete blank: complete blank. This even happens with the csv file, from dots: dots towards blank: blank. Andre Joost got around a similar problem by using semicolon delimited files, but it feels to me like this is a genuine bug in master, especially given the same files don't blank the Voronoi shapefile in DuFour: don't blank the Voronoi shapefile in DuFour. Has anyone else experienced this? I'm about to raise it on QGis hub.

Question: can I colour the Voronoi polygons using the depth value? The Voronoi shapefile has depth as a field but it doesn't do anything - possibly it doesn't know how to deal with the fact that each Voronoi polygon has a number of depths equal to its number of edges (usually 4 in my case here). Can I colour them using the depth value from the points file somehow?

  • you seem to have a regular grid, so why not convert it to raster ? Have you checked that the field you want to symbolize is of numeric type ? – radouxju Jan 19 '14 at 19:04
  • seems that it is a regular grid all over (for some reason zooming out adds weird overlaps which make it look otherwise). Raster here we come, thanks! – dez93_2000 Jan 20 '14 at 13:38
1

you can give the value of your points to your polygons using the spatial join (vector > management tools). Then you will have a depth value for all your polygons.

  • I'll try this, then the raster idea above. The benefit of this method is that it fills odd-shaped the coastal voronois with values, which the raster will only partially do. Thanks! – dez93_2000 Jan 20 '14 at 13:40

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.