With the advent of PDS4 there continues to be confusion for the Equirectangular (Equidistant Cylindrical).

First depending on the projection implementation this projection can have 3 parameters. Note for planetary we don’t use false easting or northings (and they are assumed to be 0).

PDS3 ISIS3 VICAR | PDS4 | define | PROJ | ArcMap/Envi | FGDC |
---|---|---|---|---|---|

Center Longitude | cart:longitude_of_central_meridian (required) | central meridian or Longitude of projection center | +lon_0 | Central Meridian | Longitude of Central Meridian, longcm |

Center Latitude | cart:standard_parallel_1 (required) | latitude of true scale. Defines the latitude where scale is not distorted | +lat_ts | Standard Parallel 1 | Standard Parallel , stdparll |

DNE, assumes 0 | cart:latitude_of_projection_origin (optional, assumes 0, good to be explicit though) | Latitude of projection center | +lat_0 | DNE, assumes 0 | DNE |

- DNE = does not exist. And while cart:latitude_of_projection_origin is optional, it would be good to explicitly define as 0.0
- Note Simple Cylindrical, Plate Carree is a subset (simple case) of Equirectangular where it is implied that cart:standard_parallel_1 = 0.0. For PDS4 just use Equirectangular as Simple Cylindrical is currently not available.

I have been fighting this projection for a long-while and HiRISE got caught in the middle.

Trent

- PROJ: https://proj.org/operations/projections/eqc.html
- Snyder 1987, Map Projections…: https://pubs.usgs.gov/pp/1395/report.pdf#page=103
- wikipedia: https://en.wikipedia.org/wiki/Cylindrical_equal-area_projection#Cylindrical_projections
- wolfram: http://mathworld.wolfram.com/CylindricalEquidistantProjection.html
- FGDC: https://www.fgdc.gov/csdgmgraphical/spref/horiz/planar/gridsys/acs/e.htm
- ArcMap (and Pro)/new ENVI: http://desktop.arcgis.com/en/arcmap/latest/map/projections/equidistant-cylindrical.htm
- old ticket about this: https://isis.astrogeology.usgs.gov/IsisSupport/index.php?topic=3810.msg15330#msg15330