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.. _glossary:
================================================================================
Glossary
================================================================================
.. glossary::
Ballpark transformation
For a transformation between two geographic CRS, a ballpark
transformation is a coordinate operation that only takes into account
potential difference of axis orders (long-lat vs lat-long),
units (degree vs grads) and prime meridian (Greenwich vs Paris/Rome/other
historic prime meridians). It does not attempt any datum shift, hence
the "ballpark" qualifier in its name. Its accuracy is unknown, and could
lead in some cases to errors of a few hundreds of metres.
For a transformation between two vertical CRS or a vertical CRS and
a geographic CRS, a ballpark transformation only takes into account
potential different in units (e.g. metres vs feet). Its accuracy is
unknown, and could lead in some cases to errors of a few tens of metres.
.. note::
The term "Ballpark transformation" is specific to PROJ.
Pseudocylindrical Projection
Pseudocylindrical projections have the mathematical characteristics of
.. math::
x &= f(\lambda,\phi)
y &= g(\phi)
where the parallels of latitude are straight lines, like cylindrical
projections, but the meridians are curved toward the center as they
depart from the equator. This is an effort to minimize the distortion
of the polar regions inherent in the cylindrical projections.
Pseudocylindrical projections are almost exclusively used for small
scale global displays and, except for the Sinusoidal projection, only
derived for a spherical Earth. Because of the basic definition none of
the pseudocylindrical projections are conformal but many are equal
area.
To further reduce distortion, pseudocylindrical are often presented in
interrupted form that are made by joining several regions with
appropriate central meridians and false easting and clipping
boundaries. Interrupted Homolosine constructions are suited for showing
respective global land and oceanic regions, for example. To reduce the
lateral size of the map, some uses remove an irregular, North-South
strip of the mid-Atlantic region so that the western tip of Africa is
plotted north of the eastern tip of South America.
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