FW: [Gdal-dev] GML and GDAL

[Clay, Bruce]

Frank: sorry for the previous direct mail.  I hit reply and didn't pay
attention to where it was going.



Frank and Norman:
  Thanks for your replies.

I'll give a little background and maybe from that you can tell if I am
going the wrong direction.

I have been working with the Blue Marble Viewer and am in the process of
building a similar tool as that allows us to use the Blue Marble data
sets or basic DEM / images files to provide accurate 3D scenes.  I
currently use GDAL / OGR to let the user overlay ArcView shape files on
the scene and through Demeter to load terrain files.

The original Blue Marble Viewer developer is animate that the GUI should
not be part of the visualization tool because it would slow things down
too much.  The new tool already has a DIS (IEEE 1278) interface to allow
it to be used in interactive simulations but I need to give the user
better local control of the scene to do things like overlay processed
image data over the scene and measure various aspect within the scene.

My thought was to use XML (since everyone is soooo crazy about it these
days) messages either through a local pipe or a network socket as a
control mechanism.  Since GML is a defined standard I was thinking of
using that.  I have not had time to go through the 600 GML page document
(though I am in the process of doing so) to see if it can be used this
way.

Is there a better standard protocol for doing such thing that will allow
the GIS tools to pass control and data messages or can GML be used that
way?

Thanks again.

Bruce

-----Original Message-----
From: Frank Warmerdam [mailto:fwarmerdam at gmail.com] 
Sent: Wednesday, January 26, 2005 9:53 AM
To: Clay, Bruce
Cc: gdal-dev at xserve.flids.com
Subject: Re: [Gdal-dev] GML and GDAL

On Wed, 26 Jan 2005 09:39:12 -0500, Clay, Bruce <bclay at ball.com> wrote:
> 
> Sorry if these questions are off track but it seems that the GDAL user
group
> if probably the most competent group to ask these questions. 
>  
> Can anyone describe in laymen's terms how the Geography Markup
Language
> (GML) would be used between a 3D terrain visualization tool and
external
> users? 

Bruce, 

I can imagine a few ways, but your question seems a bit peculiar.  GML
would be a reasonable format to provide view position, DEM and feature
overlay data to a 3D terrain visualization tool but of course the end
user
isn't going to be entering GML directly. 

> Does GDAL have any support for GML? 

There is an OGR driver for reading and writing GML data. It has a
variety of limitations but works reasonably well for simple GML
datasets.
Note that OGR is a feature interface.  So it is used to read GML files
full
of point, line, and polygon features.  Not raster DEMs. 

> Is there any particular reason to use or not use GML to control a GUI
less
> visualization tool from an external GUI? 

GML is a geographic data encoding format.  It could be used as an input
format to a visualization service but in general I would not imagine it
being used the way you suggest.   Of course, I am not sure what
sort of decoupling your are trying to establish between the GUI and the
backend. 

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