Two-Point Fit

The Two-Point Fit Projection is used when a local grid needs to be converted to another coordinate system. From two known points (with both easting/northing and lat/long values for each point), the remainder of the grid values can be derived and used for coordinate conversion purposes.

The "Two-Point Fit" projection has the following parameters:

• False Northing of the first point
• False Easting of the first point
• False Northing of the second point
• False Easting of the second point
• Latitude of the first point
• Longitude of the first point
• Latitude of the second point
• Longitude of the second point

The Geographic Calculator takes two points (i.e. a line) from one coordinate system (lat/long for example) and THE SAME two points from a second coordinate system (e.g. local survey coordinates) and matches them. You must have TWO points that you know what the coordinates are in BOTH systems.

Example Situation: For example: A surveyor ties into 2 benchmarks (BM1 = 45N, 84W and BM2 = 45 00 01N, 84W). She starts at BM1 and calls it 10000/10000(Northing/Easting) and traverses to BM2 and gets some N/E value. You now have two points (BM1 & BM2) that have Lat/Long coordinates and Local coordinates. That is, you now have the endpoints and orientation of a common line in two coordinate systems. You need to define a new coordinate system using those two points as the references. Any scaling, rotation, etc. issues are taken care of because you have just linked two points (i.e. defined a line length and orientation in space) that are common to both coordinate systems.