something like this will work?

So far so good. And the srs_id passes the sanity check as it is the value I would expect.

The problem comes when we get to the envelope. We know it is a double[] from the spec and we know it is Little Endian from the flag byte. The trouble I'm having is understanding how to take that information and translate it to a template for unpack. From the list in the documentation, the closest seems to be 'V' but that is a long not a float.

unpack'ing the envelope with 'V' gives these values: 

minx - 3307124816
maxx - 1092842796
miny - 867583392
maxy - 1092852469
minz - 1374389536
maxz - 1091757350

[download]
This makes no sense as min_x has to numerically less than max_x - it is only a co-ordinate system, albeit one in 3 dimensional irregular spherical space. Likewise with min_z and max_z, this is height above sea-level and the min has to numerically less than the max.

So from the data it seems I am using the wrong unpack template of 'nCCV(V)6'.

I've tried the two float options - 'f' and 'd' but they produce equally unrealistic values.

Do you have any advice on how I go about translating from the information I know about the data to the template necessary to unpack it?

buzzwords like SRSID or OSGB mean nothing to me

Sorry!

SRS - Spatial Reference System is the co-ordinate system used to identify where a point is on the Earth's surface. Many SRS's exist and none are perfect. In order that the data can be used, we need to know which SRS we are using

OSGB - Ordnance Survey of Great Britain is the SRS that we most commonly use here in the UK. Because the UK is a relatively small country, OSGB mostly ignores the curvature of the Earth. OSGB is what we have found as the SRS ID in this GeoPackage so that's a sanity check that we are on the right path so far.

In reply to Re^6: Geo Package files by Bod
in thread Geo Package files by Bod

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