McBryde-Thomas Flat-Polar Quartic – Global Mapper

The McBryde-Thomas Flat-Polar Quartic Projection is a pseudocylindrical, equal area projection. It was presented by F. Webster McBryde and Paul D. Thomas in 1949. It is primarily used for examples in various geography textbooks, and is sometimes known simply as the Flat-Polar Quartic projection.

The central meridian is a straight line 0.45 as long as the Equator. Other meridians are fourth-order (quartic) curves that are equally spaced and concave toward the central meridian. The parallels are unequally spaced straight parallel lines, spaced farthest apart near the Equator and running perpendicular to the central meridian. The poles are represented by lines one-third as long as the Equator.

Scale is true along latitudes 33°45' N and S, and is constant along any given latitude. Distortion is severe near the outer meridians at high latitudes. This projection is free of distortion only at the intersection of the central meridian with latitudes 33°45' N and S.

The "McBrydeThomasFlatPolarQuartic" Projection has the following Parameters:

Parameter Name	Parameter String	Units
Longitude of the Center of the Projection	central_meridian	AngularValue
False Easting	false_easting	LinearValue
False Northing	false_northing	LinearValue

NOTE: Only a spherical form of this projection is used. The semi-major axis of the ellipsoid (sphere) is used for forward and inverse projection from grid to geodetic coordinates within the system wherein this projection is incorporated.