How to extract the boundary of a raster image?

Question

I am working in QGIS 2.10.1 and I have the following situation: I have some Landsat8 scenes (different paths and rows) and I want to extract their boundary. My final objective is to superimpose them to the vector of my study area, so that I can show how the scenes cover the study area and in which points they overlap. I have already tried to convert the raster into a vector, but QGIS cannot make it, it crashes or it gives me back only part of the polygon.

Is there anybody who's got an idea to solve this problem?

Answer 1

You can use Plugin: Image Footprint as commented by @Mapperz. You need to download the plugin from plugin Manager, and this is how it works:

1. Specify the folder (directory) where the images are located
2. Use Valid pixels and specify the CRS of the image.
3. The outpout will create a virtual vector file with a CRS of WGS84 as the default CRS
4. You need to Save as the virtual vector file into a permanent file with the correct CRS that should be same as the image file.

Here is the input image file stored in the folder:

Here is the output footprint:

You can refer to the presentation: Qgis ibama imagefootprint for more information.

Answer 2

You can use "Create layer from extent" processing algorithm selecting the desired raster layer as extent source

Answer 3

If you have an alpha channel in you image, you can use GDAL. to be more specific gdal_polygonize.py and use the alpha band to convert to polygon

gdal_polygonize.py image.tif "boundary.shp" -b 4 -f "ESRI Shapefile" None DN

It will return a polygon layer which has two features in it. inside and outside of alpha band. delete the outside and you have an image boundary. GDAL Polygonize