[Mapbender-users] Problems with the handling of some OWS in Mapbender2 - solved

[Armin Retterath]

Hello,

the solution below is not sufficient, cause points out of a special area 
are not projected.

E.g.:
SELECT X(st_transform(GeometryFromText('POINT(-180 -90)',4326),25832));
Will allways throw an error:

ERROR:  transform: couldn't project point (-180 -90 0): latitude or longitude exceeded limits (-14)


It is not so easy to allow arbitrary transformations. Projected systems 
are normally defined for special areas. The epsg registry have 
information about the bboxes of those areas. If a transformation of a 
longlat (EPSG:4326) point (bbox) into such a local system is demand, it 
will be needed to alter the coordinates!

In following changesets a possibility is implemented to define such 
areas for projection systems in the mapbender.conf:

http://trac.osgeo.org/mapbender/changeset/8993/trunk/mapbender
http://trac.osgeo.org/mapbender/changeset/8994/trunk/mapbender

Hope this helps a little bit ;-)

Armin



On 02.07.2014 16:03, Armin Retterath wrote:
> Hello together,
>
> in some Mapbender implementations it is not possible to register 
> services, that have a global extent like -180,-90,180,90.
> It was possible without any problems under postgis 1.3.1 and proj4 4.5 
> (e.g. debian lenny), but when updating to postgis 1.5.1 in conjunction 
> with proj4.7 (e.g. debian wheezy) it  came to problems when nadgrids 
> are used to make precise coordinate transformations.
>
> The problem was the definition of the nadgrids in the epsg file and in 
> the postgis spatial_ref_sys table. Before proj4.6, someone was able to 
> define following proj4text:
>
> +proj=tmerc +lat_0=0 +lon_0=6 +k=1 +x_0=2500000 +y_0=0 +ellps=bessel 
> +units=m +nadgrids=BETA2007.gsb
>
>
> When st_transform was invoked, the transformation was done without 
> problems. In the newer version an error will occur, if the point that 
> should be transformed is not in the bbox of the nadgrid itself. The 
> spatial selects will throw an error and mapbender makes trouble ;-) .
>
> If you update to a newer postgis/proj version, you should set the @ 
> sign before the .gsb file and give a null value for the case, that the 
> gsb file is not used (e.g. the point is outside the bbox of the grid 
> or the grid file was not found).
>
> +proj=tmerc +lat_0=0 +lon_0=6 +k=1 +x_0=2500000 +y_0=0 +ellps=bessel 
> +units=m +nadgrids=@BETA2007.gsb,null
>
>
> After this you will not longer will have trouble with your postgis and 
> mapbender ;-) .
>
> SQL to update the proj4text in case of german-wide BETA2007 
> transformations (you have to download the BETA2007.gsb to the proj 
> folder before):
>
> UPDATE spatial_ref_sys set proj4text = '+proj=tmerc +lat_0=0 +lon_0=6 
> +k=1 +x_0=2500000 +y_0=0 +ellps=bessel +units=m 
> +nadgrids=@BETA2007.gsb,null' WHERE srid = 31466;
>
> UPDATE spatial_ref_sys set proj4text = '+proj=tmerc +lat_0=0 +lon_0=9 
> +k=1 +x_0=3500000 +y_0=0 +ellps=bessel +units=m 
> +nadgrids=@BETA2007.gsb,null' WHERE srid = 31467;
>
> UPDATE spatial_ref_sys set proj4text = '+proj=tmerc +lat_0=0 +lon_0=12 
> +k=1 +x_0=4500000 +y_0=0 +ellps=bessel +units=m 
> +nadgrids=@BETA2007.gsb,null' WHERE srid = 31468;
>
> UPDATE spatial_ref_sys set proj4text = '+proj=tmerc +lat_0=0 +lon_0=15 
> +k=1 +x_0=5500000 +y_0=0 +ellps=bessel +units=m 
> +nadgrids=@BETA2007.gsb,null' WHERE srid = 31469;
>
> UPDATE spatial_ref_sys set proj4text = '+proj=utm +zone=32 
> +ellps=GRS80 +units=m +datum=WGS84' WHERE srid = 25832;
>
>
> Hope that helps a little bit
>
> Armin
>


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