[Mapserver-users] WMS client re-projection errors

[Matthew Perry]

Hi folks,
  
  I have some shapefiles in UTM, NAD27, Zone 10
(epsg:26710) which I'm trying to overlay on a WMS
shaded relief layer from the USGS in Geographic, WGS84
(epsg:4326). The problem is a noticable distortion on
the y axis. Features line up at the center of the
image, but become more and more distorted as you move
above or below the center-line. 

These three images should capture the idea (keep your
eye on the peak in relation to the roads around it):

http://darkstar.rr.nu/download/mapserv1.jpg
http://darkstar.rr.nu/download/mapserv2.jpg
http://darkstar.rr.nu/download/mapserv3.jpg


It is almost as though the WMS image is vertically
compressed. However, when using a WMS image from
terraserver (nad83), the map is aligned properly. I am
running mapserver 4.2.0 on slackware linux with proj
4.4.7 & the datum shift files. Perhaps the requested
WMS extents are not accurate because of the datum
shift?? Is there something unique to shifting from
wgs84 to nad27?? Anyone have any ideas?


The abbreviated mapfile is as follows:
-----------------------------
MAP

  PROJECTION
    "init=epsg:26710"
    # UTM zone 10, Nad27, meters
  END

  LAYER
    NAME "Shaded_relief"
    GROUP "bg"
    STATUS OFF
    TYPE RASTER
    CONNECTIONTYPE WMS
    CONNECTION
"http://gisdata.usgs.net:80/servlet/com.esri.wms.Esrimap?servicename=USGS_WMS_NED&"
    METADATA
      "wms_srs"    "EPSG:4326"
      "wms_title"    "Shaded Relief"
      "wms_name"    "US_NED_Shaded_Relief"
      "wms_server_version"    "1.0.0"
      "wms_format"    "image/png"
      "wms_group_title" "background"
    END
    PROJECTION
      "init=epsg:4326"
    END
  END

  LAYER
    NAME "Roads"
    STATUS OFF
    DATA "clip1"
    TYPE LINE
    TOLERANCE 2
    DUMP true
    METADATA
      "wms_title"    "Klamath Basin Roads"
      "wms_srs"    "EPSG:26710"
      "wms_abstract" ""
      "wfs_title"   "Klamath Basin Roads"
      "wfs_srs"    "EPSG:26710"
      "wfs_abstract" ""
    END
    CLASS
      NAME "Roads"
      STYLE
        SYMBOL 1
        SIZE 2
        COLOR 0 0 0
      END
    END
  END

END
---------------------------------


Here is a link to a small, clipped shapefile if anyone
feels inclined to try it out...

http://darkstar.rr.nu/download/clip1.zip


... and the urls to recreate the three sample images
are:

http://localhost/cgi-bin/mapserv?mode=map&map=/var/www/htdocs/klamath2/klamath2.map&mapext=594418.2128140883+4727975.646318736+602962.0885061937+4733853.945029724&mapsize=610+420&layers=Roads+Shaded_relief

http://localhost/cgi-bin/mapserv?mode=map&map=/var/www/htdocs/klamath2/klamath2.map&mapext=594411.1981378223+4730115.122579895+602955.0738299277+4735993.421290884&mapsize=610+420&layers=Roads+Shaded_relief

http://localhost/cgi-bin/mapserv?mode=map&map=/var/www/htdocs/klamath2/klamath2.map&mapext=594411.1981378224+4726172.874518348+602955.0738299278+4732051.173229337&mapsize=610+420&layers=Roads+Shaded_relief

-----------------------------------

Thanks... Any ideas are greatly appreciated!!

Matthew Perry
Humboldt State University
Natural Resources Planning