Incorrect behavior in WMS-client mode

BushmanBushman Global Mapper UserPosts: 29
edited August 2008 in Bug Report
I'm trying to work with some Norwegian raster data from public WMS at
wms


In GlobalMapper 8.03 (fortunately, I din't uninstalled it) everything is OK with this server.
But when I try to work with it in 9.03, tiles appears to be "clipped" some strange same way. Server setup is equal in 8.03 and 9.03.
Here is info, how to reproduce this error:
1. Set Lat/Lon-WGS84 projection for workspace
2. Set (maybe, with some overview data) screen boundary to
WEST LONGITUDE=5.790649° E
NORTH LATITUDE=60.518444° N
EAST LONGITUDE=5.900636° E
SOUTH LATITUDE=60.478275° N
3. Set up WMS server as described above and get layer "Ortofoto alle" (it's QuickBird satellite data) for current screen bound.

And here goes the difference:
- in 8.03 tiles are cut by Lat/Lon grid (as I can see during download) and it fills screen without holes
- in 9.03 tiles are cut by some unknown grid (which is tilted strongly) and each tile has some "clipping" by lines, parallel to current projection grid. If you change scale (zoom in) clipping will change.
Unfortunately, I don't have any traffic analyser to check difference between wms requests of 8.03 and 9.03, but I think, it's a kind of problem with projection of tiles, returned by server.

Comments

  • BushmanBushman Global Mapper User Posts: 29
    edited July 2008
    I just installed CommView traffic analyser and made some experiment with exactly same territory from 8.03 and 9.03.
    Here are results:

    9.03 URI in request looks like this:
    /services/wms/wms.aspx?VERSION=1.1.1&SERVICE=WMS&request=GetMap&LAYERS=OrtofotoAlle&FORMAT=image/png&styles=&SRS=EPSG:27398&BBOX=-1256968.960,504469.503,-1256853.162,504585.301&WIDTH=512&HEIGHT=512&TRANSPARENT=TRUE
    while 8.03 URI looks like this:

    /services/wms/wms.aspx?VERSION=1.1.1&SERVICE=WMS&request=GetMap&LAYERS=OrtofotoAlle&FORMAT=image/png&styles=&SRS=EPSG:4326&BBOX=5.84092850,60.49903260,5.84189622,60.50000032&WIDTH=512&HEIGHT=512&TRANSPARENT=TRUE

    Yes, according to GetCapabilities Norge i Bilder , WMS supports EPSG:27398 = NGO 1948 (Oslo) / NGO zone VIII but why GM using it instead of something else (EPSG:4326 WGS 84, Lat/Long is not the best, but it works)?
    Especially it's a problem, because NGO Zone 8 is for 4°10'.0-wide zone along central meridian 29°03'22.500" . I think, GM just get "last non-Lat/Lon projection" from Capabilities list in this case.

    Maybe, it will be better to use some QuantumGIS-style WMS source dialog, where user can set one of supported projections from Capabilities list. I think, it will be best way, instead of some kind of "guessing" by GM. There are other normal UTM projections and Lat/Lon, as "universal" solution (remember, that using Lat/Lon always, causes information loss, because of non-square pixels).
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited July 2008
    In the later releases Global Mapper will try to use a non-Geographic projection if possible if the data is specified as supporting it as those projections will typically be less distorted than lat/lon. However in some cases the WMS servers don't seem to serve up the data properly in all projections that they claim to support.

    What you can do is force the projection to a particular one by adding a particular projection code to your service name, like 'WMS&SRS=4326'.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • BushmanBushman Global Mapper User Posts: 29
    edited July 2008
    I tried to force projection before posting message here. It's no sense, because server (according to common HTTP standards) recognize only one SRS parameter (normally - last in URI string). Any way - if WMS normally handle forced parameter, other parameters will be in conflict with it, because GM requests tiles, using NGO/TM coordinates (see captured URI examples). Projection has to be defined in GM before creating requests. You say, that GM will work with other projection than WGS84/LatLon, but problem is that GM already is requesting data in other projection (in some strange way).

    Now I have to use GM 8.03 to request data and export it to GeoTIFF as workaround.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited July 2008
    Whenever you pass additional parameters on the service name line in Global Mapper, Global Mapper parses those extra parameters out and doesn't pass them, but just uses them to affect Global Mapper's behavior. So if you use a service name of 'WMS&SRS=4326', Global Mapper will see the explicitly requested SRS value and select that as the projection to use rather than whatever projection it automatically determined.

    In any case, I have gone ahead and improved the automatic detection of a projection to use so that Transverse Mercator-based projections won't be used for data sets with a large longitudinal span as TM projections don't work well far from their central meridian.. This change causes 4326 to be chosen rather than a particular NGO zone projection. I have placed a new build at http://www.globalmapper.com/global_mapper9.zip with the change for you to try. Simply download that file and extract the contents into your existing v9.xx installation folder to give it a try.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • BushmanBushman Global Mapper User Posts: 29
    edited August 2008
    Works correctly, thanks!
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