[mapserver-users] WMS non-square extent query using openlayers

[Frank Warmerdam]

David,

MapServer is definately able to return results that are non-square,
and further that do not have 1:1 aspect ratio with the geo request
(thus resulting in requesting so called "non square pixels").  In WMS
mode I believe non-square pixel support is enabled by default - I think
this is not the case in traditional MapServer mode.

But if I were you, I'd start by examining that WMS request is actually
being generated and sent to MapServer by OpenLayers and determine
if it is doing what it ought to.

BTW, I'm surprised you are seeing "three sides" of the request and
one not being.  When MapServer fixes extents that imply non-square
pixels it would end up changing two sides (actual sides or bottom and
top) equally.

Best regards,

On Wed, Jan 25, 2012 at 2:43 PM, David Quinn <daithiquinn at gmail.com> wrote:
> Hi List,
>
> Is it possible to receive a non-square tile, or collection of tiles, from a
> WMS query? I'm using openlayers to send a WMS query based on a user-chosen
> extent of a rectangular polygon. My javascript is as follows:
>
>     WMSLayer = new OpenLayers.Layer.WMS(
>            "layerName",
>            "wms_server",
>            {layers: 'roads', },
>            {'maxExtent': polygonBounds}
>        );
>
> The initial part of my .map file is:
>
> MAP
>     NAME
>  "roads"
>     UNITS          meters
>     EXTENT       -850000 495000 -890000 500000
>     SIZE             256 256
>     STATUS       OFF
>     DEBUG        ON
>
> and I am returning information from a raster.The query returns a WMS layer
> fine, but only three of the four sides of the polygon have the correct
> extents, and the WMS layer is a square. I've tried to illustrated this in
> the below diagram:
>
> X = requested
> _____________
> |                        |
> |       XXXX       |
> |       XXXX       |
> |                        |
> ---------------------
>
> Y = returned
> _____________
> |       YYYY        |
> |       YYYY        |
> |       YYYY        |
> |                         |
> ----------------------
>
> I've tried adjusting the SIZE values but this does not seem to change the
> limit. The extents are definitely correct, as I've used them for querying
> non-WMS data that is displayed in-browser. When I subtracted a value from
> the "bound.top" value in Openlayers, the correct values were returned, but
> this did not seem like the right way to fix the problem. I'd appreciate any
> suggestions!
>
> Thanks,
> David
>
>
>
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>



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