[Freegis-list] FW: [ogdidev] Various Developments

[Matt.Wilkie]

-----Original Message-----
From: Frank Warmerdam [mailto:warmerda at home.com] 
Sent: Tuesday, September 19, 2000 9:58 AM
To: ogdidev
Subject: [ogdidev] Various Developments


Folks, 

I thought I should give people heads up of a few things I have been working
on.

 o I have incorporated support in GDAL (http://www.remotesensing.org/gdal)
for
   reading OGDI raster data.  The work is preliminary, but it makes
transparent
   use of ecs_SetRegion() to read back overview data when requested by the
   application.  

   This means that OpenEV (http://openev.sourceforge.net) can now be used as
   an OGDI raster viewer. OpenEV understands that the OGDI raster source can
   produce overviews at any level efficiently (well more efficiently than 
   loading full-res data into the application, and downsampling there).  It
   takes full advantage of this. 

 o I have implemented a simple OGDI driver for GDAL, so that I can access 
   any GDAL supported raster format from an OGDI enabled application.  I
mainly
   did this because I didn't think that any of the free OGDI drivers were
   likely to generate overviews of rasters efficiently.  The GDAL driver
will
   do so, if the underlying file has pre-built overviews.  GDAL includes 
   utilities for generating overviews for a variety of raster formats in 
   associated GeoTIFF files. 

 o Amoung other things, the above implementation include implementation of
   a PROJ.4 to OpenGIS Well Known Text projection translation module.  Code
   to translate from OGC Well Known Text to PROJ.4 format was implmented
some
   time ago. 

 o Daniel Morissette has implemented read support for OGDI vectors within my
   OGR library (a subtree of GDAL).  In theory this means that OGR enabled
   applications can read OGDI vector sources.  Daniel also recently upgraded
   the popular UMN MapServer to use OGR as one source of vector data.
OpenEV
   can also use OGR to read vectors.  While performance accessing vectors in
   MapServer through OGR and OGDI layers may not be great, it is an
interesting
   proof-of-concept of the technology. 

I must stress that my recent work on OGDI <--> GDAL compatibility is 
preliminary.  It is a proof of concept.  I haven't bundled binaries of any
of this, but the source is all in CVS.  If anyone is interested in using
some
of these capabilities they can contact me for further details on what was
done,
and how to get access to the code. 

When (if?) I get binaries of OpenEV with OGDI support built on Windows (my
work has mostly been on Linux) I will make an announement here.  

Both the work that I did, and the work that Daniel did are somewhat limited
by our ongoing problem with identifying layers available from an OGDI
datasource
automatically.  We made it possible for a user who knows what layers they
want
to get access to them, but it is not generally possible at this time to get
a
list of available layers from a data source since there hasn't yet been any
standardization of how to do this as has been discussed at length here, and
elsewhere in the past. 

Best regards,

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