[GIS] Is it possible to generate a vector polygon from a polygon on a raster image

Question

I have a raster map which I have extracted from a government report providing flood extent return frequencies. I want to 'snatch' these flood extent polygons (i.e. convert to vector) and I was wondering if there is a simple way to do this in QGIS. Simply digitising these layers by tracing new polygons would be too time consuming and potentially result in human error.

Is there a tool or methodology someone could recommend to me which would recognise these polygons in raster format (there are clearly outlined and coloured distinctly differently to the background) so I can convert them to vector?

Any help with this is very much appreciated.

Camilla

Answer 1

It can be done using the QGIS GRASS Plugin..you can use r.to.vect for your task..I found a demo video of this in youtube..It is an excellent demo..check this link

here is a snap of the tool