Transformation Settings

Using the Transformation tab of the Drawing Settings dialog box, you can relate the local northing and local easting coordinates of your drawing to the grid northing and grid easting coordinates for the current zone.

The zone transformation settings do the following:

• Relate local coordinates to grid coordinates by transforming distances measured on the Earth (or geoid) to distances on an ellipsoid.
• Relate distances on the ellipsoid to the flat plane (projection) of the current zone’s grid coordinate system.

These transformations are accomplished through the use of scaling factors. First, a sea level scale factor is applied to the local values measured on the geoid, and then a grid scale factor is applied, which relates the ellipsoid values to the grid projection. The scaling factors can be defined in two ways:

• The sea level scale factor relates the distances on the geoid to the distances on the ellipsoid.
• The grid scale factor relates the distances on the ellipsoid to the distances on the grid projection.

You must also specify reference points in establishing transformation settings.

These reference points are the two points that tie the local and grid coordinates together. The reference points can be defined in two ways:

• By the grid and local coordinates of two known reference points in your drawing.
• By the grid and local coordinates of one known point and a known rotation to grid north.