Am trying to instal BREC plugin in QGIS 2.4 and 1.8 for the purpose of automatically detect polygons (buildings) from a raster (TIF) file but i can't find that plugin, its not available in plugin library. How can I get that plugin in QGIS and its working steps?
Is there any other way to automatically find the polygons (buildings) from a raster file (TIF) in QGIS?
Answer
You might want to look at SAGA's "DTM Slope based filter", which can be used from QGIS.
This takes a DSM, and outputs two rasters
- removed objects (buildings)
- bare earth (anything which isn't a building)
If you have SAGA GIS installed, it can be called using Processing, or you can add it to the Processing Modeller. It appears in Processing panel under SAGA > Grid - Filter > DTM Filter (Slope based)
Here's an example. Original DSM on left. Buildings on right.
Once you have the rasters, you can convert them to polygons.
It's a bit more complicated than this. In real world situations the DSMs tend to be noisy. You may need to simplify them, remove gaps, reduce noise, etc. If you're just after outlines, further processing may be needed (e.g Raster Calculator)
The settings you need, and specific post-processing you need, depends on too many factors to give you a more specific answer. Hopefully this will help get you started.
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