TRMM 3B42RT product has no Coordinate Reference System?

Question

When I download TRMM precipitation product 3B42RT.2016010100.7.7day and when opening it in QGIS the raster has no CRS and is seen in another place with a smaller resolution, I already tried reprojecting and assigning it an CRS and it continues the same.

Answer 1

Let's look first at the information provided by gadlinfo for the 3B42RT.2016010100.7.7day.tif file:

C:\>gdalinfo 3B42RT.2016010100.7.7day.tif
Driver: GTiff/GeoTIFF
Files: 3B42RT.2016010100.7.7day.tif
Size is 1440, 480
Coordinate System is `'
Metadata:
  TIFFTAG_DATETIME=2016:01:05 19:28:31
  TIFFTAG_DOCUMENTNAME=./image/3B42RT.2016010100.7.7day.tif
  TIFFTAG_IMAGEDESCRIPTION=IDL TIFF file
  TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch)
  TIFFTAG_SOFTWARE=IDL 7.1.1, ITT Visual Information Solutions
  TIFFTAG_XRESOLUTION=100
  TIFFTAG_YRESOLUTION=100
Image Structure Metadata:
  COMPRESSION=LZW
  INTERLEAVE=BAND
Corner Coordinates:
Upper Left  (    0.0,    0.0)
Lower Left  (    0.0,  480.0)
Upper Right ( 1440.0,    0.0)
Lower Right ( 1440.0,  480.0)
Center      (  720.0,  240.0)
Band 1 Block=1440x2 Type=UInt16, ColorInterp=Gray

Indeed, the file does not include its Coordinate Reference System. However, on the server there is also published the world file that brings georeferencing. Its name is 3B42RT.2016010100.7.7day.tfw and its content is:

      0.2500000
      0.0000000
      0.0000000
     -0.2500000
   -179.8750000
     59.8750000

If we check again the information of the GeoTIFF file, having in the same folder both files with the same name as they are provided, we see that GDAL recognizes the georeferencing:

C:\>gdalinfo 3B42RT.2016010100.7.7day.tif
Driver: GTiff/GeoTIFF
Files: 3B42RT.2016010100.7.7day.tif
       3B42RT.2016010100.7.7day.tfw
Size is 1440, 480
Coordinate System is `'
Origin = (-180.000000000000000,60.000000000000000)
Pixel Size = (0.250000000000000,-0.250000000000000)
Metadata:
  TIFFTAG_DATETIME=2016:01:05 19:28:31
  TIFFTAG_DOCUMENTNAME=./image/3B42RT.2016010100.7.7day.tif
  TIFFTAG_IMAGEDESCRIPTION=IDL TIFF file
  TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch)
  TIFFTAG_SOFTWARE=IDL 7.1.1, ITT Visual Information Solutions
  TIFFTAG_XRESOLUTION=100
  TIFFTAG_YRESOLUTION=100
Image Structure Metadata:
  COMPRESSION=LZW
  INTERLEAVE=BAND
Corner Coordinates:
Upper Left  (-180.0000000,  60.0000000)
Lower Left  (-180.0000000, -60.0000000)
Upper Right ( 180.0000000,  60.0000000)
Lower Right ( 180.0000000, -60.0000000)
Center      (   0.0000000,   0.0000000)
Band 1 Block=1440x2 Type=UInt16, ColorInterp=Gray

Everything seems to indicate that it is an Equirectangular projection. Even so, the information can be ambiguous. We do not know the datum on which the coordinates are referred. For that we must refer to the Documentation:

Knowing that the datum is WGS84, we already have all the necessary information about the CRS of the dataset.

---

Link within the documentation of the GDAL library on georeferencing for the GeoTIFF file format driver:
https://gdal.org/drivers/raster/gtiff.html#georeferencing

Article about world files on Wikipedia:
https://en.wikipedia.org/wiki/World_file