Pitney Bowes MapXtreme - Manual (Page 580)

Appendix H: Elements of a Coordinate System
Projection Datums
MapXtreme v7.1 587 Developer Guide
Standard Parallels (Conic Projections)
In conic projections a cone is passed through the earth intersecting it along two parallels of latitude.
These are the standard parallels. One is to the north and one is to the south of the projection zone.
To use a single standard parallel specify that latitude twice. Both are expressed in degrees of
latitude.
Oblique Azimuth (Hotine Oblique Mercator)
When specifying a great circle (Hotine Oblique Mercator) using a point and an azimuth (arc), the
azimuth is called the Oblique Azimuth and is expressed in degrees.
Scale Factor (Transverse Mercator)
A scale factor is applied to cylindrical coordinates to average scale error over the central area of the
map while reducing the error along the east and west boundaries. The scale factor has the effect of
recessing the cylinder into the earth so that it has two lines of intersection. Scale is true along these
lines of intersection.
You may see the scale factor expressed as a ratio, such as 1:25000. In this case it is generally
called the scale reduction. The relationship between scale factor and scale reduction is:
scale factor = 1-scale reduction
In this case the scale factor would be 1-(1/25000) or 0.99996.
False Northings and False Eastings
Calculating coordinates is easier if negative numbers aren’t involved. To eliminate this problem in
calculating State Plane and Universal Transverse Mercator coordinates, it is common to add
measurement offsets to the northings and eastings. These offsets are called False Northings and
False Eastings. They are expressed in coordinate units, not degrees. (The coordinate units are
specified by the Units parameter.)
Range (Azimuthal Projections)
The range specifies, in degrees, how much of the earth you are seeing. The range can be between
1 and 180. When you specify 90, you see a hemisphere. When you specify 180 you see the whole
earth, though much of it is very distorted.
Polyconic Projection
The following description is copied from Map Projections – A Working Manual, USGS Professional
Paper 1395, by John P. Snyder.
The Polyconic projection, usually called the American Polyconic in Europe, achieved its name
because the curvature of the circular arc for each parallel on the map is the same as it would be
following the unrolling of a cone which had been wrapped around the globe tangent to the particular
parallel of latitude, with the parallel traced onto the cone. Thus, there are many (“poly-”) cones
involved, rather than the single cone of each regular conic projection.