[Mapserver-users] WMS client re-projection errors

[Tyler Mitchell]

Is the image crossing UTM zones?
I recall reading something very recently that says Proj couldn't handle 
datum shifts, but may now.  I'm not sure that's the issue though.

mapserver-users-admin at lists.gis.umn.edu wrote on 07/13/2004 12:31:20 PM:

> 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
> 
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