How to find lat/lon values for every pixel in a GeoTIFF file?

Question

I want to a store GeoTIFF file pixel by pixel in the database. I need to store pixel values along with the lat/lon of that pixel on the GeoTIFF image. Is it possible to do that?

Answer 1

This may be a bit archaic: Convert the pixels to points, add lat and long fields, and populate with lat and long values.

Answer 2

The world file (.tfw) that accompanies a GeoTIFF contains:

• pixel size in the x-direction (and y-direction) in map units/pixel and
• x-coordinate (and y-coordinate) of the center of the upper left pixel. This is all you need to calculate position in Lat/Lon of every pixel.

Answer 3

In a generic sense, use the affine transform parameters, which should be available with any raster file format. With GDAL, this is available with GetGeoTransform(), or PostGIS' ST_GeoReference() function. After finding these six parameters, one only needs to determine which ones they are, then a function can be made to transform in linear space.

E.g., with Python:

from osgeo import gdal
ds = gdal.Open('myfile.tif')

# unravel GDAL affine transform parameters
xoff, a, b, yoff, d, e = ds.GetGeoTransform()

def pixel2coord(x, y):
    """Returns global coordinates from pixel x, y coords"""
    xp = a * x + b * y + xoff
    yp = d * x + e * y + yoff
    return(xp, yp)

For example, if there is a pixel at x=10, y=22, then it's real-world coordinates are:

>>> pixel2coord(10, 22)
(2780000.0, 6162300.0)

Something similar can be cooked up for PostGIS with ST_Affine().