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Glossary

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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.

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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.

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Note

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The term “Ballpark transformation” is specific to PROJ.

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Pseudocylindrical Projection

Pseudocylindrical projections have the mathematical characteristics of

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+\[ \begin{align}\begin{aligned}x &= f(\lambda,\phi)\\y &= g(\phi)\end{aligned}\end{align} \]
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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.

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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.

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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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