Uncompress/decode files with magic type xV4 (78 56 34)

I’m trying to decode what should be a digital elevation model file (probably, from the file size a 2500 by 2500 int16 binary file), but it is somehow compressed, with magic type 78 56 34. Does anyone have an idea to uncompress this kind of files? I found a similar question here (by BillS), but that one wasn’t answered yet.

I’ve tried to decode a bit of the header, but I only got as far as finding the magic type (xV4 -> Photocap template) and number of bytes (12503448 in bold) to follow:
Here’s the first few hex-bytes of the file.
70170000701700000A0000001E000000
0E745A3AF1D8FFFFD5FF313235303334
343800A24A0488C9BE00010000007856
34125D00000001000000050000000047
800D3C56778C6B5A67CC2AB7F74BD151

A big thanks in advance!