Did an aerial drone survey and have generated a mosaic and .shp file with the elevation and contour data using Pix4D. However, some of the areas elevations are off because the elevations represent the top of the canary grass in those areas.

I would like to be able to subtract approx. 4 feet from the elevations in those areas. Is this possible. If it is, could you outline the steps as I am still learning QGIS.

  • Does the mosaic include height information or only the shapefile? – Simbamangu Sep 25 '16 at 5:37
  • The shapefile from Pix4D contains the elevations which I add to the mosaic layer. I will look at a video or two to learn how to use the rasterize tool on a polygon. The goal is to create a polygon around the canary grass that will allow me to adjust the elevation of the Pix4D shapefile where it intersects the polygon as described by Freight_Train – FlyingPhotos Sep 25 '16 at 19:08

Create a polygon around the area that you want and create an attribute with the height you want to subtract.

Convert this to a raster using the Rasterize tool - this is found in the Raster toolbar in the conversion section. Here you select the attribute field you want to use and then the output raster resolution.

Then using the raster calculator subtract this new raster from the original.

  • Thanks, that got me started. I was able to create a polygon and to shade it but that is as far as I got. Because I am still learning, I don't know how to do the other steps. Would you mind adding a little more detail or if you happen to know of a tutorial on the topics? Thanks – FlyingPhotos Sep 24 '16 at 21:18

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.