STAR*NET V6 - Circe

Chapter 10 Adjustments in Grid Coordinate Systems
The “Hotine” projection, used in a few places in the world, is a modified Mercator
projection sometimes called “Oblique Mercator.” It includes a latitude and longitude
defining its origin, a azimuth of its central axis and a scale along this “skew azimuth.”
The azimuth is defined by its tangent value. The sample file list illustrates use of this
projection type by parameters that would define the Zone 1 in Alaska.
A zone name may contain up to 18 characters including any internal blanks, and is
terminated by a “:” colon character. Each custom zone requires an ellipsoid to be
designated. Its name must be one from the ellipsoid list described above and it must be
spelled exactly the same.
When entering scale factors for either a Transverse Mercator (“T”) line, the Lambert
(“L”) line or the Hotine (“H”) line, the scale value may be entered as either a ratio or a
factor. A value less than 2.0 (i.e. 0.99992345 or 1.000334567) will be interpreted as a
factor. Any value of 2.0 or greater will be taken as a scale ratio denominator as
commonly used in the United States (15000 meaning 1 part in 15000).
Therefore, for example, scale values entered as 10000 and 0.9999 have exactly the same
meaning: (10,000-1 part)/10,000 = 9999/10,000 = 0.9999.
Scale values 1.0 and 0.00 are both interpreted as 1.0 (scale of unity).
In the STAR6.CUS file, all angular entries (Central Meridian, Latitude of Origin, North
and South Latitudes) are entered in “packed” DMS format (DDD.MMSSsss). The
Latitude of Origin for Colombia which is 04-35-56.570 N, for example, would be entered
as 4.355657. Latitudes south of the equator and longitudes west of Greenwich must be
entered as negative.
Custom Linear Units
These optional definition data lines are needed only if you wish to enter linear data
(coordinates, distances, etc.) in units other than those already built into the program
which include US Feet, International Feet, and Meters. Units defined in this file will be
added to the available linear units already built into the program and will appear in the
“Units” selection list of your Project Options/Adjustment dialog. A unit line begins with
a “U” character and includes its name and the ratio of the unit to the meter. The name of
the unit may be up to 8 characters and is terminated by a “:” colon character. We have
supplied two custom units as examples, however they have been “commented out” so
that they won’t show up in your Project Options unless you want them to.
In the STAR6.CUS file, all linear values are entered in meters! The program
automatically performs any conversions necessary to conform to units you are actually
using in a project.
Refer to the listing of the STAR6.CUS file shown on the following page for notes
pertaining to the data described above. The file contains many comment lines, those
beginning with the # character, and is meant to be self documenting.
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