Loading rasters using raster2pgsql

raster2pgsql is the default tool for importing rasters to PostGIS. Even though GDAL itself does not provide means to load rasters to the database, raster2pgsql is compiled as a part of PostGIS and therefore supports the very same formats as the GDAL version appropriate for given version of PostGIS.

raster2pgsql is a command-line tool. In order to review its parameters, simply type in the console:

raster2pgsql

While taking a while to get familiar with the raster2pgsql help is an advised approach, here are some params that worth highlighting:

• -G: Prints a list of GDAL formats supported by the given version of the utility; the list is likely to be extensive.
• -s: Sets the SRID of the imported raster.
• -t: Tile size - expressed as width x height. If not provided, a default is worked out automatically in the range of 32-100 so it best matches the raster dimensions. It is worth remembering that when importing multiple files, tiles will be computed for the first raster and then applied to others.
• -P: Pads tiles right / bottom, so all the tiles have the same dimensions.
• -d|a|c|p: These options are mutually exclusive:
  • d: Drops and creates a table.
  • a: Appends data to an existing table.
  • c: Creates a new table.
  • p: Turns on prepare mode. So no importing is done; only a table is created.
• -F: A column with raster name will be added.
• -l: Comma-separated overviews; creates overview tables named o_<overview_factor>_raster_table_name.
• -I: Creates GIST spatial index on the raster column.
• -C: Sets the standard constraints on the raster column after the raster is imported.

For the examples used in this section, we'll use Natural Earth's 50M Gray Earth raster.

As you remember, ogr2ogr has a ogrinfo tool that can be used to obtain the information on a vector dataset. GDAL's equivalent for raster files is called gdalinfo and is as worthy as its vector brother:

gdalinfo GRAY_50M_SR_OB.tif

You should get a similar output:

Driver: GTiff/GeoTIFF
Files: GRAY_50M_SR_OB.tif
       GRAY_50M_SR_OB.tfw
Size is 10800, 5400
Coordinate System is:
GEOGCS["WGS 84",
    DATUM["WGS_1984",
        SPHEROID["WGS 84",6378137,298.257223563,
            AUTHORITY["EPSG","7030"]],
        AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich",0],
    UNIT["degree",0.0174532925199433],
    AUTHORITY["EPSG","4326"]]
Origin = (-179.999999999999970,90.000000000000000)
Pixel Size = (0.033333333333330,-0.033333333333330)
Metadata:
  AREA_OR_POINT=Area
  TIFFTAG_DATETIME=2014:10:18 09:28:20
  TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch)
  TIFFTAG_SOFTWARE=Adobe Photoshop CC 2014 (Macintosh)
  TIFFTAG_XRESOLUTION=342.85699
  TIFFTAG_YRESOLUTION=342.85699
Image Structure Metadata:
  INTERLEAVE=BAND
Corner Coordinates:
Upper Left  (-180.0000000,  90.0000000) (180d 0' 0.00"W, 90d 0' 0.00"N)
Lower Left  (-180.0000000, -90.0000000) (180d 0' 0.00"W, 90d 0' 0.00"S)
Upper Right ( 180.0000000,  90.0000000) (180d 0' 0.00"E, 90d 0' 0.00"N)
Lower Right ( 180.0000000, -90.0000000) (180d 0' 0.00"E, 90d 0' 0.00"S)
Center      (  -0.0000000,   0.0000000) (  0d 0' 0.00"W,  0d 0' 0.00"N)
Band 1 Block=10800x1 Type=Byte, ColorInterp=Gray

Before we get down to importing the raster, let's splits into four parts using gdalwarp utility. This way, we'll be able to show how to import a single raster and a set of rasters:

gdalwarp -s_srs EPSG:4326 -t_srs EPSG:4326 -te -180 -90 0 0 GRAY_50M_SR_OB.tif gray_50m_partial_bl.tif
gdalwarp -s_srs EPSG:4326 -t_srs EPSG:4326 -te -180 0 0 90 GRAY_50M_SR_OB.tif gray_50m_partial_tl.tif
gdalwarp -s_srs EPSG:4326 -t_srs EPSG:4326 -te 0 -90 180 0 GRAY_50M_SR_OB.tif gray_50m_partial_br.tif
gdalwarp -s_srs EPSG:4326 -t_srs EPSG:4326 -te 0 0 180 90 GRAY_50M_SR_OB.tif gray_50m_partial_tr.tif

For each command, you should see a similar output:

Creating output file that is 5400P x 2700L.
Processing input file GRAY_50M_SR_OB.tif.
0...10...20...30...40...50...60...70...80...90...100 - done.

Having prepared the data, we can now move onto importing it.