Problems with mapserver and oblique projections

[Arnd Wippermann]

Hello,

I have also played with some unusual projections and have entcountered the
same problem. I use mapserver 4.10 and as interface OpenLayers (on to
different machines). Some tiles look good, others not drawn at all or only
parts. Also differs the output on both servers. Zooming and the visible
layers effect also the output.

Here the example with epsg:44065
http://gis.ibbeck.de/ginfo/ibbOLClient/OpenlayersClient.html?MAPNR=11801&LAY
ERS=11500&ZOOM=0&CENTER=0,0

And some others
http://gis.ibbeck.de/ginfo/ibbOLClient/OpenLayersClient.html?KARTE=10504
http://gis.ibbeck.de/ginfo/ibbOLClient/OpenlayersClient.html?MAPNR=12800&LAY
ERS=11500&ZOOM=0&CENTER=1660129.823,-415032.456
http://gis.ibbeck.de/ginfo/ibbOLClient/OpenlayersClient.html?MAPNR=12400&LAY
ERS=11500&ZOOM=4&CENTER=-1426674.0662,-622548.6834


I have looked at many different projections and mostly there were no
problems with the output. 

http://gis.ibbeck.de/ginfo/ibbOLClient/OpenlayersClient.html?MAPNR=12300&LAY
ERS=11500&ZOOM=0&CENTER=0,0

The blue screen layer is a shape with 30 degree lines (therefor it looks a
bit wrong sometimes), the grids all 1 degree lines.

Arnd Wippermann
http://gis.ibbeck.de/ginfo/ibbOLClient/OpenlayersClient.html


-----Ursprüngliche Nachricht-----
Von: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] Im
Auftrag von Trond Michelsen
Gesendet: Mittwoch, 15. November 2006 16:25
An: MAPSERVER-USERS at LISTS.UMN.EDU
Betreff: [UMN_MAPSERVER-USERS] Problems with mapserver and oblique
projections

Hi.

I'm having some problems getting mapserver 4.4.1 to draw maps in an oblique
projection.

Here's an example:

http://wms.met.no/cgi-bin/mapserv?map=../vhosts/mercator/conf/google.map&LAY
ERS=kart,cdc,base.LATLON&TRANSPARENT=false&BGCOLOR=0x99B3CC&EXCEPTIONS=appli
cation/vnd.ogc.se_inimage&FORMAT=image/png&SERVICE=WMS&VERSION=1.1.1&REQUEST
=GetMap&STYLES=&BBOX=-180,-90,180,90&WIDTH=800&HEIGHT=400&SRS=EPSG:44065
( http://tinyurl.com/ykem3c )

(red coastlines are drawn by mapserver, the grey land, the bluish coastlines
and the gridlines are drawn by an internal WMS-server.)

As you can see, mapserver omits most of the shapes close to the North Pole,
and there are some wrapping issues at the south pole. 

the proj-definition looks like this:

+proj=ob_tran +o_proj=eqc +lon_0=0 +o_lat_p=25 +a=57.29577953604224884
++b=57.29577953604224884 +no_defs <>

(the bizarre minor and major axis sizes are used to get
pseudo-decimaldegrees as units. I should probably use some scaling parameter
instead, but I was unable to find something that corresponds to the -m
command line parameter)

and my map is configured like this in the mapfile:

LAYER
  name "cdc"
  data "cntry00"
  status on
  type polygon
  PROJECTION
    "+proj=latlong"
    "+a=6371000"
    "+b=6371000"
  END
  CLASS
    STYLE
      outlinecolor 255 0 0
    END
  END
END


If the tilting is more severe, even more countries are left out of the
plot:

http://wms.met.no/cgi-bin/mapserv?map=../vhosts/mercator/conf/google.map&LAY
ERS=kart,cdc,base.LATLON&TRANSPARENT=false&BGCOLOR=0x99B3CC&EXCEPTIONS=appli
cation/vnd.ogc.se_inimage&FORMAT=image/png&SERVICE=WMS&VERSION=1.1.1&REQUEST
=GetMap&STYLES=&BBOX=-180,-90,180,90&WIDTH=800&HEIGHT=400&SRS=EPSG:44090

With no tilt at all, you basically get regular latlong coordinates, and now
all countries are being displayed:

http://wms.met.no/cgi-bin/mapserv?map=../vhosts/mercator/conf/google.map&LAY
ERS=kart,cdc,base.LATLON&TRANSPARENT=false&BGCOLOR=0x99B3CC&EXCEPTIONS=appli
cation/vnd.ogc.se_inimage&FORMAT=image/png&SERVICE=WMS&VERSION=1.1.1&REQUEST
=GetMap&STYLES=&BBOX=-180,-90,180,90&WIDTH=800&HEIGHT=400&SRS=EPSG:44000

Does anyone know what I'm doing wrong? Is there something I can do to get
mapserver to plot all countries in this projection? (Preferrably without the
wrapping issues).

--
Trond Michelsen