[Gdal-dev] Anyone heard of ESML? (maybe off-topic)

[Frank Warmerdam]

Chris G. Nicholas wrote:
> I'm know I'm dense, but can someone please explain what inherent 
 > advantage this newfangled XML shtuff has over plain 'ole looking
 > at the file suffix (.tif, .bil, .jp2, .hdf, .shp, .ppm, .sid, etc),
 > which one will have to do anyway?
> 
> and then again, (for you old timers!) there was (and still is!) a file's "magic" number.  'man magic' on a *NIX
> system yields:
> 
> "NAME magic - file command’s magic number file

Chris,

While useful, the "magic" technology has it's limitations.  Though generally
GDAL tries a similar approach where I first try to classify files by looking
for various magic values.  It doesn't help for actual raw files though, for
which ESML would be one approach to describing.


> I am facing something similar with my OpenGIS WMS service - when one clicks 
 > on an image for "FeatureInfo" - what do I return?
> 
> At this point, I am inclined to return a GlobeXplorer tracking_id, with XML 
 > schema scoped to com.globexplorer, with hooks to "drill-down" into that
 > tracking_id for schema and values.

The feature info capability of WMS is notoriously open ended, and hence
verging on useless from an interoperability point of view.

However, your approach seems reasonable. I would encourage you to go the
extra step to ensure make return XML actually be valid GML.   I gather
the tracking id you refer to would be an id for the raster dataset from
which the view (or the pixel clicked on) was derived?  If so, it would be
nice to return a GML feature with a polygon geometry representing the
footprint of the dataset as a whole, and then various other details about
the dataset as feature attributes.

Of course, you might get better advice on this on the wms-dev mailing list.
I know there have been a number of discussions of featureinfo issues there.

Best regards,

-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent