On 11-10-18 10:19 PM, Etienne Tourigny wrote:
Hi Frank,
On Tue, Oct 18, 2011 at 7:22 PM, Frank Warmerdam<[email protected]> wrote:
On Tue, Oct 18, 2011 at 1:10 PM, Etienne Tourigny
<[email protected]> wrote:
2) Change to a default south-up orientation for NetCDF data
Etienne,
Could you expand on this a bit? In particular I'm wondering if:
1) Is a south-up file represented as south up to GDAL applications?
That is, will geotransform[5] be negative or positive?
Files created by the driver have a negative pixel height
(geotransform[5]) when opened with GDAL , so I guess that means it
looks like it is north up.
When the driver opens a south-up file, it has to invert the y axis
upon import to make it compatible with GDAL's data model.
For example, a gtiff landsat that has the following geo info:
Origin = (625970.000000000000000,8981830.000000000000000)
Pixel Size = (30.000000000000000,-30.000000000000000)
Which is the same when translated to netcdf and the netcdf is read by GDAL.\
Etienne,
OK, it seems that to applications the change to producing
bottom-up files will not be particularly disruptive.
For what it gives, here are some numbers for gdal_translate on a test
dataset (22239 x 33359 INT) . The netcdf creation takes longer than
gtiff, but the difference between south-up and north-up is small.
gtiff-> gtiff
real 0m34.251s
user 0m1.550s
sys 0m3.710s
gtiff->netcdf (BOTTOM_UP=YES)
real 1m3.869s
user 0m2.520s
sys 0m5.300s
gtiff->netcdf (BOTTOM_UP=NO)
real 1m35.077s
user 0m3.050s
sys 0m6.150s
gtiff->netcdf (driver in svn trunk, north-up)
real 2m4.186s
user 0m5.110s
sys 0m7.130s
I'm a bit confused about the above. How are the "driver in svn trunk,
north-up" case and the "BOTTOM_UP=YES" case different? Why is
"BOTTOM_UP=NO" case slower than "BOTTOM_UP_YES" case?
In any event, at least for this case the differences aren't devastating
and there are options to control what is done. I am supportive of changes
that produce a more interoperable result.
As PSC chair I will not be offended if you proceed with netcdf changes
*without* a formal RFC type vote on the changes. The changes are fixing
bugs and don't cause real backward compatability issues and I'm willing to
treat you as the authority/owner for the driver.
Best regards,
--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up | Frank Warmerdam, [email protected]
light and sound - activate the windows | http://pobox.com/warmerda
and watch the world go round - Rush | Geospatial Software Developer
_______________________________________________
gdal-dev mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/gdal-dev
