dataset extents from MapServer CGI

[Bob Basques]

Frank,

My preference is to provide a layer list (one or few layers in my use 
case) and get the extents of all the layers in the list.  Either 
seperately or as a composite extent.    A XML output would be good for 
example, but not required.  I could build a wrapper to do a composite 
from an individual list if a composited version is too much overhead.

My use case: 

My Client application deals with layers on an individual basis with 
separate calls, etc.:

    * I would like to have a displayable layer (user controlled) in my
      client application that shows the extent of a particular layer. 
    * This same capability allows me to gray out a layer that is turned
      on, but not visible in a current View.
    * This would also allow me to filter for layers that are out of
      bounds and not request them automatically (as I do now) and and up
      displaying a blank image.  A definite performance enhancement I think.
    * An addidtional feature I would like to add to my client is a
      Reference image/map, that shows the layer extents.  This would be
      used as a thumbnail in a layer metadata lookup/popup.

Some WishList things (not really expected near term):

    * Using a bounding polygon vs a rectangle.
    * Feature counting (We've been over this feature with Steve L a
      couple of times), basically a method of counting features in a layer.
          o Further enhancement, would be to be able to count the
            features inside of a mapext.
    * Adding in Layer (data source) feature lists (metadata kinds o f
      things that could be derived by MapServer, either by examining the
      data or the file/db that contains it.
          o Date of sourced data (last update in a DB environment)
          o TYPE (Raster, Line, Polyline, Polygon, etc.)

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

Some possible thoughts/solutions I had on the subject:

    * Set up some commandline utility that can generate the extents from
      a layer(shpfile) list as a new layer specifically related to
      Spatial metadata (actually this idea has a bunch more too it, that
      goes beyond this topic). This new layer could be queried for all
      the appropriate info, it would also allow for adding in some
      additional link mechanisms that would be layer based.
    * Use the previous setup to build this type of data layer by default
      as a setup feature of MapServer.  Again there are some other
      things here that could obviously be added to an indexing system
      like this.  Possible use some sort of MapServer Configuration step
      periodically to keep the extents layer up to date.
    * Don't know if/when I would be able to get to it, but I would build
      this in PERL/MapScript myself if it's not plausible to include in
      MapServer.

bobb


Frank Warmerdam wrote:
> Jan Hartmann wrote:
>> I second that question. If not, could it be implemented? Very useful 
>> feature
>>
>> Jan
>>
>> Bob Basques wrote:
>>> All,
>>>
>>> Is there any way to get a dataset extents from MapServer CGI 
>>> directly (no Mapscript)?
>
> Jan / Bob,
>
> How would you see this working?  Would it be a request made against a
> particular layer?  Against the map as a whole?  Internally in the code we
> have:
>
> int msLayerGetExtent(layerObj *layer, rectObj *extent)
>
> which calls the data source specific GetExtent function.  But I don't 
> think
> this works for raster layers.  There is also msOWSGetLayerExtent() which
> first consults the layer metadata for extents.  Perhaps this would be the
> logical place to look?
>
> Well, I suppose the other side of this is that for WMS and WCS the layer
> and coverage descriptions include extents already.  Is that sufficient 
> for
> your needs?
>
> Best regards,
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