Spectra Precision FAST Survey Reference Manual - Manual (Page 113)

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your goal is to work on the specified state plane, UTM or other grid coordinate system, and you are planning to use
a one-point localization, then the scale factor should be set to 1, unless you are trying to match “ground”
coordinates, where the coordinates are “true north” but not “true scale”. In all other cases, matching ground
coordinates with GPS is best accomplished with a multi-point rover-based localization. The resulting “effective”
scale factor multiplier will appear in the localization screen, such as the 0.999779 value shown in the last figure.
After a change in a localization file, any points measured in the field by GPS will be converted from Lat/Long to local
coordinates by using the new localization file. For this reason, it is a good idea to re-convert older GPS measurements
to the same, compatible coordinate system by going to Process Raw Data, option Process GPS, within the COGO tab.
Geoid Files
The Geoid file is loaded onto SurvCE using Carlson X-Port. You first select the area of interest, then X-Port “carves
out” the geoid for that area and downloads it to SurvCE. You set the Geoid file in the EQUIP tab in the main menu and
then tap Localization. In the Localization routine, tap the GPS tab and then tap the Geoid File button. The Geoid
should be used principally with one-point localizations. Starting with a known position for the base (or using a
one-point rover localization and approximate base position), the program will add or deduct the geoidal separation from
the computed Z value on all measurements, and will match more closely to geoid-based surface elevations. The Geoid
can also be used with multiple-point rover localizations, since the added accuracy provided by the geoidal calculation
can reduce vertical residuals. This is true, however, only if the points being matched had Z values that, themselves,
considered the geoid. Since you will get a best-fit plane that minimizes vertical residuals with or without use of the
geoid, it is often not used with rover-based localizations.
Changing or Updating the Localization File
There are two ways to change a localization file. One method is to edit an existing file by deleting elements, and the
second is to add additional localization points. In either case, whenever a change in the “.dat” localization file is
detected, you are prompted whether you would like to re-process any previously stored GPS points found in the raw file.
The dialog below appears.
If you answer Yes, you will be directed to the Process GPS command found within COGO, Process Raw File.
Recalculating Stored GPS Points
There is no requirement to survey all localization points first, unless you are doing stakeout. For simple topo or data
gathering, you can set up your base, survey in one or two localization points with the rover, then gather data in Store
Points
as needed. As you move cross country and encounter another known, or unexpected, control point, you can
localize on it and add it to the list. The next step would be to verify residuals, and if the results are good, you can
reprocess the raw file and keep your entire survey fully updated. If the residuals are disappointing, you can choose not
to include the new point in the localization file. Either remove it or turn its H and V components off. You can also
choose Process Raw File to recalculate all GPS measurements at any time.
Including the Base Position in the Localization File
To use the base in the localization, you should configure the base with the Use Local Coordinates option under From
Known Position
. Here, you configure the base by entering the local point (5000,5000,100, etc.) and start a new
localization file (or use an existing one if it applies). Then, at your rover, you can add more points to the localization as
necessary.
Localization and the Raw File
If the scale for GPS is determined from the localization, a “GPS Scale” record of 1.0 and a “Localization Scale” equal
to the calculated scale appearing in the Localization screen will be written to the RW5 file.
Using the Localization File to Improve Base Localizations through Logging Static Data
The Localization File (.dat) typically applies to rover-based localizations. But if you did a Read GPS on your base
antenna position and then took GPS shots with no rover localization, and logged static data on the base in the meantime,
it is possible to submit that logged information to the OPUS program and obtain an accurate base position. At this