Rather than hardcoding assumptions or conclusions about what the machine is now, why not future-proof it? All you have to do is add the < to the unpack string to force the d (double) to be little-endian, no matter what architecture you happen to be running on. So my $minx = unpack ("d<", substr($geo,8,8)); will force it to be little-endian interpretation. (Or better, since your code already has access to that bit in the fourth byte, use logic based on that bit to determine whether your envelope's unpacks use "d<" or "d>" , so that you can handle input files that made either choice for the envelope: 
my $unpack_string = ($flag&0x1 == 0x1) ? "d<" : "d>"; 
... 
my $minx = unpack($unpack_string, substr($geo,8,8));

[download]

But given that your CPU is little endian, that is what your unpack from Re^4: Geo Package files already showed a value of: 637590.385 is the correct value based on the 8 bytes 50 b8 1e c5 2c 75 23 41 : that is little-endian-double for 637590.385 . The problem is that you don't believe that number is correct. But since you have not apparently tried sanity-checking your interpretation with another tool, like swl suggested in Re^9: Geo Package files, you don't know if your belief is founded in reality or not. Maybe the "min" and "max" in the bounding box might not match the "min" and "max" of the values of the coordinates as stored; the portion of the spec I read wasn't clear on what the min and max were interpreted as. Or maybe the data set you were given just mis-used "min" vs "max". A sanity check in another tool is really going to help you out.

But based on the spec you have shared, and the 16 bytes you have shared, I am confident that 637590.385 is the valid interpretation of those bytes.

(I had wanted to say most of this last week, but I kept only thinking about it when I was in a crunched-for-time or on-my-phone-browser-so-read-only situation.... and then with the week-long pause, I forgot to come back.)

In reply to Re^9: Geo Package files by pryrt
in thread Geo Package files by Bod

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