Central Meridian: A straight line.
Meridians: Complex curves spaced equally along the Equator and each parallel, and concave toward the central meridian.
Parallels: The Equator is a straight line. All other parallels are nonconcentric circular arcs spaced at true distances along the central meridian.
Poles: Normally circular arcs, enclosing the same angle as the displayed parallels.
Symmetry: About the Equator or the central meridian.
polyconstd implements the Polyconic projection directly on a reference ellipsoid, consistent with the industry-standard definition of this projection. See polycon for an alternative implementation based on rotating the rectifying sphere.
For this projection, each parallel has a curvature identical to its curvature on a cone tangent at that latitude. Since each parallel has its own cone, this is a "polyconic" projection. Scale is true along the central meridian and along each parallel. This projection is free of distortion only along the central meridian; distortion can be severe at extreme longitudes. This projection is neither conformal nor equal-area.
By definition, this projection has no standard parallels, since every parallel is a standard parallel.
This projection was apparently originated about 1820 by Ferdinand Rudolph Hassler. It is also known as the American Polyconic and the Ordinary Polyconic projection.
landareas = shaperead('landareas.shp','UseGeoCoords',true); axesm ('polyconstd', 'Frame', 'on', 'Grid', 'on'); geoshow(landareas,'FaceColor',[1 1 .5],'EdgeColor',[.6 .6 .6]); tissot;