Hi Again, I have found tree solutions for my problems- Can anyone tell me if they are correct.
I clip the DTM with the polygon and the use the SAGA Real surface area. It gives me a new raster where the pixelvalues has changed from Z to a calculated area. Finally I use the Zonal statistic and add the SUM value to the polygon. The second is a Grass function r.surf.area It gives me an area in the log. The functions has a slightly different result, but it´s only 3/1000 :-) ---------- For calculating the fence I had to be a bit more old school. Distance= SQRT((x2-x1)^2 + (y2-y1)^2 + (z2-z1)^2) I took the polygon and converted it to points with a ordered pointnumber. Used the SAGA function Add Grid Values to Point It takes the Z Value from the DTM and add an attribute to a new pointlayer. The pointlayer is saved as CSV. It gives me a table with x,y and z. And in Spreadsheet I can easily calculate the length af each vertice and make a sum. :-) Regards Lene Fischer ------------------------------ Sendt: 31. januar 2016 17:52 Til: qgis-user Emne: [Qgis-user] Calculating area and length from DTM Hi, Today I have been out collecting data with my GPS in an area with huge differences in heights. My length and area will be from the "flat" area and not accurate/correct. If a contractor should order a fence - it would be too short.... :-O How do I calculate correct when I have the polygon and a terrain model. Regards Lene Fischer _______________________________________________ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: http://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user _______________________________________________ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: http://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user