Hi John,
I found some time to include jhlabs code for Stereographic and
Transverse Mercator into ncSrc-4.2.zip . The Stereographic code had
some
bugs, as you expected, and the TransverseMercator code worked well.
The
files in unidataCommon include a main method with some smaller tests.
I tested the code with toolsUI and the topography-files in
http://pastebin.met.no/p/c/file?id=8553484f24/topoFiles.zip
(those files will be automatically deleted in 14days)
The stereograhpic files have a difference of approx. 5km in southern
Norway, while the UTM files have a difference of more than 10km there
comparing the spherical vs the ellipsoid version.
I made a least effort approach when converting the code, so it's far
from well tested or beautiful. But I hope this code can make it to the
netcdf-java, if just as intermediate solution until the one or other
geo-api has been added.
Best regards,
Heiko
On 2010-06-09 23:47, John Caron wrote:
Hi Heiko:
Im not sure how fast i can get to that. Do you have real datasets
with
those projections?
The proj4 code is from the jhlabs partial port at
http://www.jhlabs.com/java/maps/proj/index.html
The ones that ive already done are at
http://svn.unidata.ucar.edu/repos/common/java/trunk/src/main/java/ucar/unidata/geoloc/projection/proj4/
I should warn you that I have seen bugs in the Java, which i think is
some automatic C/Java translater. I have been checking against the
original C code. Also, theres a lot of modifications to be made to
make
it compatible with our Projection class. Thats why the Geotools
API may
be a better idea.
BTW, Transverse Mercator on the ellipsoid i think is UTM, which we
have.
So perhaps you only need Stereographic ?
John
On 6/9/2010 7:08 AM, Heiko Klein wrote:
Hi John,
when we discussed the issue of ellipsoid-support in netcdf-java
back in
March in the mailing-list it went very fast to: use one or another
GeoAPI.
This sounded to me like a lot of work for you. If you don't plan
to do
this work in the near future (i.e. 2010), could you please send
me the
proj4j source. Maybe I can try then to add ellipsoid support of
Stereographic and Transverse Mercator to netcdf-java (4.2) during
summer.
Best regards,
Heiko
On 2010-03-24 17:46, John Caron wrote:
Heiko Klein wrote:
Hi Jon,
I just found some time to look at the source of netcdf-java
4.1. As far
as I can see, only some projections (LambertConformalConicEllipse,
AlbersEqualAreaEllipse, UTM) support ellipsoids, while the
others use a
constant spherical earth with EARTH_RADIUS = 6371.229km
In particular, Stereographic projection doesn't support
ellipsoids, so
this explains the offset in my maps.
Would be nice to have this assured by one of the
unidata-developpers. I
mainly checked the ucar/unidata/geoloc/projection sources.
Best regards,
Heiko
Yes, correct. We are slowly adding ellipsoid support, but only
after we
have a sample dataset that uses them. We are porting code from
proj4,
its rather time-consuming to get it right.
if you have sample data where the ellipsoidal earth matters,
send it
along, we'll get to it when we can. or, if you have resources and
expertise to port the proj4j code, i could send that to you and
get you
started.
John
On 2010-03-10 14:38, Jonathan Blower wrote:
Hi Heiko,
This is a good question. ncWMS relies on netcdf-java for
converting
coords to wgs84 lat lon, so I'm copying this to the mailing
list in
the hope that someone can enlighten me about ellipsoid support
in the
library.
Cheers, Jon
-----Original Message-----
From: Heiko Klein<address@hidden>
Sent: 09 March 2010 08:54
To: Jonathan Blower<address@hidden>
Subject: ncWMS and ellipsoid-support in CF-1.2
Hi Jon,
I currently try to visualize some satellite ice-maps over the
north-pole
with ncWMS, but the data seems to be displaced by some 10-30km
compared
with the land-maps (generated by mapserver).
While geo-tools and therefore ncWMS support lots of coordinate
reference
systems for the presented maps, the support for ellipsoids was
only
added to CF-1.2. Do you know if ncWMS already supports the CF-1.2
features like semi_major_axis/semi_minor_axis for input-files,
or does
it assume the CF-1.0 spherical earth with 6371km radius?
Best regards,
Heiko
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Dr. Heiko Klein Tel. + 47 22 96 30 00
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Norwegian Meteorological Institute http://www.met.no
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