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reprojection

Added by Jay Su almost 4 years ago

Hello,

I have 4 questions.

The geographic coordinates of the following projections can be generated without the attribute proj_params, if all other attributes are available:
• rotated_latitude_longitude
• lambert_conformal_conic
• lambert_azimuthal_equal_area
• sinusoidal
• polar_stereographic

Q1: What are the additional params needed for those? For example, lambert_conformal_conic asks for longitude_of_central_meridian and latitude_of_central_meridian.

I set the grid file:
gridtype = projection
xsize = 72
ysize = 46
xfirst = -180
xinc = 5
yfirst = -90
yinc = 4
grid_mapping_name = lambert_conformal_conic
longitude_of_central_meridian = 180
latitude_of_central_meridian = 45

But it still complained: latitude_of_central_meridian missing! Q2: how to fix it?

Q3: for any given projection, are there any constraints on xsize/xfirst/xinc etc?

Q4: how to implement other projections such as Mercator etc.

Thanks,
Jay


Replies (1)

RE: reprojection - Added by Uwe Schulzweida almost 4 years ago

Hello Ray,

The required projections parameters are described in the CF convention.
Here is the description for the lambert projection (https://cfconventions.org/cf-conventions/cf-conventions.html#_lambert_conformal):

grid_mapping_name = lambert_conformal_conic

Map parameters:

  • standard_parallel - There may be 1 or 2 values.
  • longitude_of_central_meridian
  • latitude_of_projection_origin
  • false_easting - This parameter is optional (default is 0)
  • false_northing - This parameter is optional (default is 0)

So the CDO error message is wrong, the parameter latitude_of_projection_origin and standard_parallel are missing.
xsize/xfirst/xinc define the projection coordinates. These usually have metric units such as meters or kilometers. So xunits and yunits must also be set accordingly.

The Mercator Projection is defined by the following parameters:

grid_mapping_name = oblique_mercator

Map parameters:

  • azimuth_of_central_line
  • latitude_of_projection_origin
  • longitude_of_projection_origin
  • scale_factor_at_projection_origin
  • false_easting - This parameter is optional (default is 0)
  • false_northing - This parameter is optional (default is 0)

These parameters are not evaluated by CDO. So an interpolation is only possible with the attribute proj_params. How this parameter looks like for the respective projections can be found in the notes to the projections in the CF convention.

Cheers,
Uwe

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