Spectra Precision FAST Survey Reference Manual - Manual (Page 108)

p106
must directly type in the desired Ground to Grid Factor.
GPS Tab
The GPS tab is where you define the RTK methods, geoid file, and GPS scale factor. The geodi
 RTK Method (Transformation Types)
: The transformation can be by plane similarity, rigid body, or
seven-parameter Helmert methods. Plane Similarity and Rigid Body both use a best-fit least-squares transformation.
The difference is that the rigid body method does a transformation with a translation and rotation, without scale.
The plane similarity does a rotation, translation and scale. These two methods only apply when two or more points
are held horizontally in the points tab. The Helmert method requires the user to enter the seven parameters on the
BY HELMERT tab.
 RTK Method (North Type)
: This option applies to the rotation when using one-point localization. For this
alignment method, the state plane coordinate is translated to the local coordinate. Then the rotation can use either
state plane grid north or geodetic north.
 Use Grid to Ground (Scale Factor for GPS)
: For most applications, the Scale Factor should be set to 1.0 to work
on the grid coordinate system using GPS. The scale factor represents the “combined” grid/elevation factor that
reduces ground distances to grid. Therefore, for GPS, the scale factor acts as a divisor. All GPS coordinates will
also be divided by the scale factor. In this way, the same “ground to grid” number can be used to convert total
station shots to the grid, or alternately to convert GPS shots to the ground. Icons allow you to "Read from GPS" to
obtain the local position or calculate the Grid to Ground factor using the Calculate icon.
To match the coordinates of any standard transformation (e.g. UTM, NAD83), the scale factor should be set to 1.0.
When configured to total stations, the Calculate option will calculate the combined grid/elevation factor from any
entered coordinate—based on your current state plane zone setting. This can allow you to go “ground to grid,” to
reduce the distance measured by total station to the sea level grid distance of GPS. If set to a GPS configuration,
Calculate
becomes Read GPS . The Read GPS option is grayed out if a multi-point localization is active. In that