Spectra Precision FAST Survey Reference Manual - Manual (Page 109)

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case, the scale factor is fixed by the localization itself, and is the inverse of the value appearing in localization,
because within Units, we display the “ground to grid” number, whereas in localization, we display the “grid to
ground” multiplier. For base or one-point rover localizations, Read GPS applies. After converting the
LAT/LONG from the GPS to the state plane coordinates and computing the grid and elevation factors, the Scale
Factor is applied as the final adjustment to the coordinates. This adjustment is used on the X and Y coordinates, but
not Z. In GPS, the Scale Factor is applied by dividing the distance between the coordinate and a base point by the
Scale Factor. The coordinate is then set by starting from the base point and moving in the direction to the
coordinate for the adjusted distance.
The base point is the first point appearing in the GPS Localization option. If there are no points specified in
Localization, then 0,0 is used as base point. The Scale Factor can be entered directly or calculated using the grid
factor and elevation for the current position. When using the current position, the program will read the
LAT/LONG from the GPS receiver. The scale factor is then calculated as: (State Plane Grid Factor -
(Elevation/Earth Radius)). A scale factor can be used to make grid-to-ground conversions between identical points.
This is useful if you want to adjust the lesser sea level distances of GPS to the ground (greater) distances measured
by total stations whenever you are above sea level. The grid to ground scale factor is lower at higher elevations
because it acts as a divisor (the scale factor is always defined as “ground to grid”). In summary, when configured to
GPS, the scale factor (typically <1) can be used to go “grid to ground” through division, and when configured to
total stations, the scale factor (typically <1) can be used to go “ground to grid” through multiplication. It can also
be used for any other scaling purpose desired, but be advised that any scale factor used for GPS is used as a divisor.
Because there are two potential uses of the scale factor (to adjust GPS measurements and to adjust total station
measurements), two distinct scale factors are stored and recalled for any job, one for total stations located on the TS
tab and one for GPS located on the GPS tab.
 Geoid Separation File
: This option will incorporate the geoid undulation in determining the orthometric elevation
of the measurement. The definition of the geoid model as currently adopted by the National Geodetic Survey is the
equipotential surface of the Earth's gravity field which best fits, in a least squares sense, global mean sea level.
Orthometric elevation measurements are used in survey calculations. In order to convert ellipsoid heights (He) as
measured by GPS into orthometric elevations (Eo), you must provide for a correction between the GPS-measured
ellipsoid (reference ellipsoid) and a constant level gravitational surface, the geoid. This correction is the geoid
undulation (Ug). Use XPort or SurvCOM to download the Geoid Separation File. This option only has significant
impact with one-point alignments. The zip file containing the Geoid Files (GSF, Geoid99 or EGM) is found on the
FAST Survey installation CD, and a portion of any such file can be specified (by size and center point) for
downloading to the data collector using Carlson X-Port or Carlson SurvCom.
How To Use Geoid Files with Carlson SurvCE
1.
Download and/or install either Carlson X-Port or SurvCOM to the desktop computer.
2.
Download and/or install “CarlsonGeoidGrids.exe” to a location on your desktop computer (Typically installed to
the “…\Program Files\Carlson X-Port\” directory).
3.
If you have Microsoft ActiveSync already installed on your computer, make sure that it is not currently occupying
the COM port.
To do this:
Launch ActiveSync and select Connection Settings from the File menu.
Remove the check box that refers to the port you intend to use with Carlson X-Port (Typically COM1).
Select OK to exit Connection Settings and close ActiveSync.
4.
Connect your handheld device to your desktop computer using a serial cable.