gives the difference between the angle from north to direction β on the geo grid obtained with projection proj and the actual angle from north to direction β at location loc.


gives the difference between projected and unprojected angles from direction α to direction β.

Details and Options

  • Geo grid direction difference is a measure of how much angles between geo directions get expanded or contracted during map projection.
  • GeoGridDirectionDifference[proj,loc,αβ] computes the difference angle (-)-(β-α) where α, β are azimuths defined on the Earth at the given location loc, and , are the respective projected bearings on the map.
  • GeoGridDirectionDifference[proj,loc,α] is equivalent to GeoGridDirectionDifference[proj,loc,0α].
  • GeoGridDirectionDifference[proj,loc] computes the largest absolute value of GeoGridDirectionDifference[proj,loc,αα+90] for any value of α.
  • A geo projection can be given as a named projection "proj" with default parameters or as {"proj",params}, where "proj" is any of the entities of GeoProjectionData and params are parameter rules like "StandardParallels"->{33,60}. GeoProjectionData["proj"] gives the default values of the parameters for the projection "proj".
  • The location loc can be given as a coordinate pair {lat,lon} in degrees, a geo position object like GeoPosition[] or GeoGridPosition[] or as a geo entity Entity[].
  • The bearing or azimuthal direction α is an angle measured clockwise from true north. It can be given as a Quantity angle, as a number in degrees or as a named compass direction like "North", "NE" or "NEbE".
  • GeoGridDirectionDifference threads over its location and direction arguments.
  • Possible options of GeoGridDirectionDifference include:
  • GeoModelAutomaticmodel of Earth or a celestial body


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Basic Examples  (1)

Compute the angular difference induced by the Mollweide projection in the eastward direction at New York:

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The angle between the projected north and east directions is about 27.7° smaller than the original 90°:

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Scope  (9)

Options  (1)

Properties & Relations  (6)

Possible Issues  (1)

Neat Examples  (1)

Introduced in 2019