[Proj] D-Sat 1 coordinates

Robert Jaeschke robert-j at gmx.de
Sat Mar 26 06:11:55 EST 2005


On Thu, Mar 24, 2005 at 04:45:23AM +0200, Mikael wrote:

> You should consider the possibility that the coordinates might actually
> be stored as floating point numbers.

Thank you for that objection!

> Suppose the coordinates are stored as doubles and the first eight bytes
> are the easting and the next eight bytes the northing.
> For a few test cases we get these coordinates:
> Alsenz 414510.2 5516851.0
> Alt Golm 850099.6 5814692.5
> Alt Rehse 776849.4 5942433.0
> Alt-Schadow 839608.2 5793427.0

I can reproduce these values. But I'm still suprised, that it works.
Because in long float format the first two bytes (AFAIR 12 bit) should
store the exponent. And there are many cities with the first four bytes
equal to zero. The same applies to bytes 9-11, which should hold the
exponent of the northing - they're all zero. 
I'll have to check the IEEE-BFPA-Standard again.

> Let's assume the coordinates are in zone 3. 

Should be zone 4, so +4500000. But this gives values above 50, which is
way to much. Nevertheless:

> The results are shifted a few kilometers to north, but still, I think
> they seem somewhat promising.

I updated the home page: the floats give us again a map of Germany. But
the difference to screen or real coordinates is still not constant. 

Regards, Robert

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