I have a SRTM30 tile named E140S10.gif attached, containing 600 column and 750 rows. The upper left corner is 140° W, thus +140 and 10°S, thus -10, according to the filename...
In a text editor, I tried to create a georeferenced file .gfw (attached):
0.066666666 0.000000 0.000000 -0.066666666 140 -10
I calculated the 0.06666666 by dividing 40° (width of the tile) / 600 pixels = 0.0666666666
and 50° (height of the tile) / 750 pixels = 0.0666666666
The gfw seems correct and has the same name as the .gif file, located in the same directory, but do not open in ArcMap. I get an error "missing spatial reference...".
I don't understand why?