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Re: [udig-devel] World Mercator with postgis
Hello Jody,

I found part of the problem: the postgis definition of 3395 contains

"  PARAMETER["latitude_of_origin",0],"

in the srtext.  Removing this makes it recognizable in uDig.

Thanks,
David

On Thu, Feb 12, 2009 at 3:15 PM, Jody Garnett <jody.garnett@xxxxxxxxx> wrote:
David Zwarg wrote:
Hi Jody,

Thanks for the response.

I am having difficulty adding my own SRID, and getting uDig to recognize it.  What I really want is to be able to support this in my own custom application, but for now, I am running uDig from Eclipse -- I don't know if that changes things.

This is what I've done: I created a geometry table in PostGIS, and set the SRID to 3395 (the SRID in PostGIS for "WGS 84 / World Mercator").  When I load the layer into uDig, the CRS is set to 4326.  That didn't work.
When you right click on the layer (or better yet go to the catalog and find the table) and ask for more information what does it tell you? The GeoTools library we use does go and check the WKT definition from postgis.

The definition of 4326 may match what you were trying to set up?

Next, I created a geometry table in PostGIS, and set the SRID to 41001 (the SRID in uDig for "WGS84 / Simple Mercator" -- this is nearly the same, and would suit my purposes if it would work).  When I load the layer into uDig, the CRS is set to 4326.
For any definition that is not complete (say from a shapefile or something) we try and look up the offical EPSG definition and find a match; could this be what is happening to you?

I assumed that the problem was that PostGIS and uDig had to have the same CRS in both their systems, so the SRID in the PostGIS spatial_ref_sys table matches the EPSG code in uDig's Coordinate System dialog.  Sure enough, if I set the PostGIS spatial reference to something else (for my test, I used EPSG:4269), then when it loads into uDig, the CRS is set correctly.

Additionally, when I attempt to add the definition from PostGIS (the srtext from the spatial_ref_sys table) for 3395 into the Custom CRS box in uDig, I can press "Apply" and "OK" to my heart's content, but the dialog never closes, and I can't get out of the dialog without canceling.

The custom CRS dialog box is just consulting uDig internal list of definitions; there are facilities for you to add more definitions to uDig at a coding level (you can set up a little property file with additional definitions). Before we go that far ... can you compare what you are trying to do with the definition of 4326?

Please advise,
David


On Wed, Feb 11, 2009 at 6:42 PM, Jody Garnett <jody.garnett@xxxxxxxxx <mailto:jody.garnett@xxxxxxxxx>> wrote:

   Mark Leslie is the postgis guy I know these days and he can
   confirm or deny what I say here :-)

   You can add your own SRID codes to to PostGIS and define one th be
   generic cartesian 2D if you like. UDig will pick up this WKT
   definition and be fairly happy.

   In uDig you click to change the projection; there are two tabs
   (one where you select the formal epsg definition from a list; and
   a second where you can type in your own WKT). You can also right
   lick on a layer and "force" a change of projection (if the data
   source is wrong for example - it does happen).

   Mercator is supported in our referencing library so you should be
   able to proceed resonably well. Normally PostGIS SRID codes line
   up with the EPSG codes ...

   Jody

   David Zwarg wrote:

       Hello,

       I am wondering if there is a way to use the World Mercator
       projection in PostGIS in uDig.  I am unable to use either the
       PostGIS (3395) or the uDig (41001) EPSG codes for world
       mercator in my PostGIS layer -- they both show up as Generic
       cartesian 2D.  As soon as I attempt to add geometry and edit
       geometry, uDig goes into an endless loop of
       IllegalArgumentExceptions.

       However, if I use an EPSG code that appears in BOTH postgis
       and uDig, it seems to work alright.  If there was a way to
       represent Generic cartesian coordinates in PostGIS, that would
       be preferable, but -1 causes this same
       IllegalArgumentException spiral.  Am I missing a general
       projection that would be more suitable?

       Also, during this experiment, I was unable to create a custom
       CRS in the uDig map preferences, or by clicking on the button
       in the status bar.  How do you create a custom CRS from a
       known WKT?

       Thanks,
       David
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_______________________________________________
User-friendly Desktop Internet GIS (uDig)
http://udig.refractions.net
http://lists.refractions.net/mailman/listinfo/udig-devel
 

_______________________________________________
User-friendly Desktop Internet GIS (uDig)
http://udig.refractions.net
http://lists.refractions.net/mailman/listinfo/udig-devel

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