This tutorial explores some basic raster operations in QGIS such as viewing, mosaicing and subsetting.
We will download some public domain raster data for Brazil and view it in QGIS. Next, we will merge these into a single mosaic and clip it using a country boundary to get a single seamless dataset for the country.
We need Brazil country boundary to clip our raster. You can get the Admin 0 - Countries shapefile from Natural Earth.
NASA/GSFC, Rapid Response site has a good collection of near real-time satellite imagery. A good regional product is USDA Foreign Agricultural Service (FAS) subsets.. We will use 2km resolution FAS subsets for Brazil for this tutorial.
Here is how to search and download the revelant data.
Repeat the process for all 7 FAS subsets for Brazil.
For convenience, you can directly download sample data used in this tutorial from links below.
Ctrlkey and click on the image files to make a multiple selection. Click Open.
The Raster menu in QGIS comes from a core plugin called GdalTools. If you do not see the Raster menu, enable the GdalTools plugin from . See Using Plugins for more details.
Ctrlkey and select all the. subsets. Now click Select... next to Output file and name the output as
Brazil_mosaic.tif. At the bottom, check the box next to Load into canvas when finished. Click OK.
ne_10m_admin_0_countries.zipfile and click Open. When prompted to select the layer within the zip file, select
ne_10m_admin_0_countrieslayer and select Save Selection As....
brazil_boundary.shpand make sure Add saved file to map box is checked. click OK.
Brazil_mosaic. Name the Output file as
Brazil_mosaic_clipped. In the Clipping mode section, choose Mask layer. Select the newly created
brazil_boundaryas the mask layer. Check the box next to Load into canvas when finished. Click OK.
Brazil_mosaic_clippedlayer and select Properties.