So I've been trying to convert a georeferenced Tif raster file into a vector shp file using QGIS. It's seems to complete this but it ends up giving me a feature class that has over 500,000 features, almost like it's creating a row per pixel. So with that many features it's very hard to work with and when I do finally get it to Classify like into 8 classes of natural breaks, it doesn't look like the original tif file. My end goal is to only have a few (less than 20) polygons based off the raster not thousands. Could it be that the Tif file I'm using is already pre-processed or something?
[GIS] Convert a Tif raster file to vector shp file in QGIS
convertqgisraster
Best Answer
It sounds as if your raster needs to be classified, which you can do using the experimental Sextante toolbox.
Each pixel in a one-band raster has a value attached to it and using GRASS v.reclass from the Sextante toolbox allows values to be grouped into classes. Say for example I have a raster with values of between 0 and 1400; using v.reclass I could group the values into seven classes, using this 'rules' text file:
The output would be a new raster having a value of 1 for all of the values of between 0 and 200 in the original raster, of 2 for all of the values between 201 and 400 in the original raster, and so on.
Once classified, the raster could then be polygonised.
Nick.