Usage

The Marp class contains all functions for converting between geodetic, Apex, and MARP coordinates. Note that Marp inherits the Apex class, so all Apex functions are also available through Marp.

Initialize the Marp Class

The Marp class requires a date, reference height, and either the location of the MARP north pole or null island ((0,0) point) when initialized. The date can be provided as a decimal year, date object, or datetime object. The reference height defaults to 0 km when not specified. A list of three floating point values should be provided for either pole or null. For pole, this should be the latitude and longitude of the new MARP north pole, plus and additional angle that the coordinate system should be rotated around that new pole so that the prime meridian falls in the correct location. For null, this should be the latitude and longitude of the new MARP null island, plus the bearing direction of North from that point. The coords keyword defines whether the pole or null positions are specified in Apex or geodetic coordinates (default Apex). If the position is specified in geodetic coordinates, alt should be used to specify the point’s altitude above the Earth’s surface (defaults to the reference height). Some examples are provided below.

Specify location of north pole in Apex coordinates.

import marppy
import datetime as dt
M = marppy.Marp(dt.datetime(2021,7,31), poll=[54.7,33.8,10.0])

Specify location of null island in geodetic coordinates.

import marppy
M = marppy.Marp(2019.4, null=[74.7,-94.9,26.0], alt=300., coords='geo')

Note: For most use cases, specifying null will be most intuitive.

Convert between Apex and Marp Coordinates

Use the apex2marp() and marp2apex() functions to convert between Apex and Marp coordinates.

mlat, mlon = M.apex2marp(65.0, 17.0)
print(mlat, mlon)
31.567175854041146, 12.261423536020837

alat, alon = M.marp2apex(31.6, 12.3)
print(alat, alon)
64.95365215608916, 17.00718613610059

Convert between Geodetic and Marp Coordinates

Use the geo2marp() and marp2geo() functions to convert between geodetic and Marp coordinates. Note that height must be specified when converting to and from geodetic coordinates.

mlat, mlon = M.geo2marp(84.3, -136.8, height=450.)
print(mlat, mlon)
8.116045001238708, -7.773699770282615

glat, glon, _ = M.marp2geo(8.1, -7.8, height=450.)
print(glat, glon)
84.31710052490234, -137.10552978515625