[Mapserver-users] Raster: rotation params in WLD file

[Ed McNierney]

Marian -

I think you might double-check to make sure you're solving the right
problem.  You say that your source map does not have North as up.  For
many standard map projections, North is not normally up - this is part
of the map projection and is expected.

If you could give us a little more information about the input map
you're working with, and some info about what exactly you want your
output result to be, then we'll figure out the best solution AND help
you use it!

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
Phone: (978) 251-4242  Fax: (978) 251-1396
ed at topozone.com


-----Original Message-----
From: Marian Grigoras [mailto:mgrig at mnet-online.de] 
Sent: Saturday, February 22, 2003 2:59 PM
To: Frank Warmerdam; UMN MapServer
Subject: Re: [Mapserver-users] Raster: rotation params in WLD file

Hello Frank,

> If W[i] is one of lines 0 through 5 of the world file you can
calculate
> the georeferenced location of pixel [Xr,Yr] as:
>
>   Xgeo = W[4] + W[0] * Xr + W[2] * Yr
>   Ygeo = W[5] + W[4] * Xr + W[3] * Yr

I have to admit I did not get the logic behind these formulas.
Intuitively I would say that at least Xr and Yr should be
switched in the Ygeo formula, but don't waste time on explaining if
I am wrong, this is pure speculation.

The point is that I need to understand the real significance af these
parameters, as I will have to compute them for my maps.
What I actually need is to be able to define a rotation around the
Z axis, that is to specify that my new Oy axis makes "alfa" degrees with
the North direction.

You posted once the info in a GeoTIFF, containing a 4x4 matrix:
W(0)    W(1)    0    W(4)
W(2)    W(3)    0    W(5)
0            0        0        0
0            0        0        1
which leads me to the idea that you multiply something like:
[Xgeo Ygeo Zgeo ?]' = (4x4) * [Xr Yr Zr ?]'
where [A]' is the transpose of A.
Is this correct?

I also found a post suggesting to use Proj
(http://mapserver.gis.umn.edu/data2/wilma/mapserver-users/0201/msg00146.
html
). Is this the way to do it?
If yes, is LCC the only projection that can be used?

> Note that MapServer does not support producing rotated map results.
They
> are always north up.
Does this mean that if I am able to define a deviation from North,
the map will come out rotated? ("always North up")

Sorry if some questions are trivial, but I do not have a background in
geographical coordinate systems. If you know some documents that might
explain these rotation coefficients, please give me a link. Thanks.

Best regards,
marian


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