[Openev-discuss] Reprojection

[Frank W. <war...@ho...>]

Andrew,

I have prepared a small example script for reprojection:

#!/usr/bin/env python

import osr

srs = osr.SpatialReference()

srs.SetProjCS("My UTM")
srs.SetAttrValue("PROJCS|PROJECTION", "Transverse_Mercator")
srs.SetProjParm("latitude_of_origin",0)
srs.SetProjParm("central_meridian",-81)
srs.SetProjParm("scale_factor", 0.9996)
srs.SetProjParm("false_easting",500000)
srs.SetProjParm("false_northing",0)
srs.SetWellKnownGeogCS( "WGS84" )
srs.SetLinearUnits("meter",1.0)

srs_ll = srs.CloneGeogCS()

print srs
print srs.ExportToPrettyWkt()
print srs_ll
print srs_ll.ExportToPrettyWkt()

ct = osr.CoordinateTransformation(srs, srs_ll)

print ct.TransformPoint( 444000, 3000000 )

This shows doing things pretty much the hard way.  In particular, setting
the projection parameters one at a time by name.

The full list of projection transformation methods, and their parameters
can be fetched using the new osr.GetProjectionMethods() call.  It returns
a list of projection methods.  

eg. 
>>> import osr
>>> pm_list = osr.GetProjectionMethods()
>>> print pm_list[0]
('Transverse_Mercator', 'Transverse Mercator', [('latitude_of_origin', 'Latitude of Origin', 'Lat', 0.0), ('central_meridian',
'Central Meridian', 'Long', 0.0), ('scale_factor', 'Scale Factor', 'Ratio', 1.0), ('false_easting', 'False Easting', 'm', 0.0),
('false_northing', 'False Northing', 'm', 0.0)])
>>> 

The format for a projection method is:

 ( name_of_projection_method, user_visible_name_of_projection_method,
   list_of_parameters)

each parameter in the list_of_parameters look like:

  ( parameter_name, user_visible_parameter_name, type, default_value )

The types are "Long", "Lat", "Angle" (for skew and azimuth values), "m"
(for false easting and northing), and "Ratio" for scale values.  This
should be enough to populate a GUI.

Note that there are a number of other ways to instantiate SpatialReference
objects, including based on an EPSG coordinate system id, and by ingesting
a "well known text" format description of the whole coordinate system. 

Later,

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