[netCDFJava #FQF-323932]: Help on AlbersEqualArea

Hi Nihat,

Sorry for the delay in responding to you. You can find the code for our 
implementation of AlbersEqualArea here:
https://github.com/Unidata/thredds/blob/master/cdm/src/main/java/ucar/unidata/geoloc/projection/AlbersEqualArea.java

It's based on "Map Projections Used by the U.S. Geological Survey". See 
https://pubs.usgs.gov/bul/1532/report.pdf

Does that help? If you can identify a bug in a reproducible manner, we'd be 
happy to fix it.

Cheers,
Christian


> Hi
> 
> I am reading Fire related data set that is defined on a projection field
> as defined in the comment section in the code snippet below. I used
> ucar.unidata.geoloc.projection.AlbersEqualArea to project my latlon
> points onto this field to see where my points lie in different fire
> zones. In closer inspection, I realized that my points are about
> 30km north from where they are supposed to be over California. If
> I project fire data onto latlon plane, I see the same issue but
> this time polygons are displaced by about 30km southward. I was
> thinking maybe earth radius was defined a little bit different
> but explicit definition of earth radius is still giving me the same
> problem.
> 
> What do you think I am missing here? I couldn't locate the source
> code to see what exactly going on. I saw a version of the source code at
> 
> https://github.com/orbisgis/cts/blob/master/src/main/java/org/cts/op/projection/AlbersEqualArea.java
> 
> but this seemed a bit different version than what I use.
> 
> Any help is greatly appreciated.
> 
> Thanks
> 
> nc
> 
> import ucar.unidata.geoloc.LatLonPoint;
> import ucar.unidata.geoloc.LatLonPointImpl;
> import ucar.unidata.geoloc.ProjectionPoint;
> import ucar.unidata.geoloc.ProjectionPointImpl;
> import ucar.unidata.geoloc.projection.AlbersEqualArea;
> import ucar.unidata.geoloc.projection.proj4.AlbersEqualAreaEllipse;
> 
> public class TestProj {
> 
> public static void main(String[] arg) {
> /*
> PROJCS["NAD_1983_Albers",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",
> SPHEROID["GRS_1980",6378137.0,298.257222101]],
> PRIMEM["Greenwich",0.0],
> UNIT["Degree",0.0174532925199433]],
> PROJECTION["Albers"],PARAMETER["False_Easting",0.0],PARAMETER[
> False_Northing",-4000000.0],
> PARAMETER["Central_Meridian",-120.0],
> PARAMETER["Standard_Parallel_1",34.0],
> PARAMETER["Standard_Parallel_2",40.5],
> PARAMETER["Latitude_Of_Origin",0.0],
> UNIT["Meter",1.0]]
> 
> */
> 
> double radius = 6378137d;
> double False_Easting = 0.0;
> double False_Northing = -4000000.0d;
> double Standard_Parallel_1 = 34.0;
> double Standard_Parallel_2 = 40.5;
> double Latitude_Of_Origin = 0.0;
> double Central_Meridian = -120;
> AlbersEqualArea prj = new AlbersEqualArea(Latitude_Of_Origin, 
> Central_Meridian, Standard_Parallel_1, 
> Standard_Parallel_2,False_Easting,False_Northing,radius);
> LatLonPoint ptl = new LatLonPointImpl(37d,-119d );
> 
> ProjectionPoint pt = prj.latLonToProj(ptl);
> 
> System.out.println(pt.getX() + " " + (pt.getY()));
> 
> Nihat Cubukcu


Ticket Details
===================
Ticket ID: FQF-323932
Department: Support netCDF Java
Priority: High
Status: Closed
===================
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