Spectra Precision FAST Survey Reference Manual - Manual (Page 112)

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Note that in this example, it takes three horizontal control points, active “H On = Y” to get horizontal residual
results, and four vertical control points, active “V On = Y” to get vertical residual results. You can employ trial and
error to remove different points from consideration both vertically and horizontally and watch the residuals of the
remaining control points improve or degrade. In this way, if you have four or more total control points, you can
determine the best combination to use as horizontal and vertical control.
 Load
: This allows you to load any localization file for modifying or for the purpose of associating it to the current
job. Note that the OK button must be used if the intention is to associate the loaded file to the current job.
 Monitor
: Goes to the standard Monitor screen. This is particularly useful to verify the quality of your satellite
coverage and your fixed or float status. You always want the best possible fixed status when conducting a
rover-based localization.
 Save
: Allows you to save the control points in a file.
 2 pt Rotate Only
: Allows you to use the second point in the localization file for direction but not for scaling. In
this case, any scale factor set on the UNITS tab in Job Settings would be active.
 OK:
Pressing OK will temporarily recall the current Localization as you work. If you change the Localization file,
Save
, then Cancel, the original Localization file will still be active. Pressing OK is what makes it active, and
current. In this case, you would need to Load the new Localization file and press OK to make it active. You can
choose to Add localization points midway on a job, and not actually use them by pressing Save, then Cancel. Then
when the job is complete, you can recall the Localization file with all the old and added localization points, go to
Process Raw File
, and re-calculate all surveying points according to the new Localization.
Discussion of Localization Techniques
If you do a base localization by entering Latitude and Longitude or known coordinates on the designated coordinate
system, then you do not need to add localization points. A base localization would put you on grid north and grid scale
and would work for any new job where you are not trying to match existing coordinates. However, any time you are
working on a project that has existing coordinates, you will most likely need to do a Localization. Even if that existing
job is supposedly on state plane, UTM or another known coordinate system, the project coordinates often fail to match
grid scale and grid north exactly, requiring localization. When localizing, it is advisable to use at least three points for
horizontal control and four points for vertical control, in order to get a measure of residuals (or accuracy). The program
will “best fit” a plane through all activated (H=On and/or V=On) control points. The residuals are how much each
activated point is off of the plane surface. Because multiple elevation points may create a slightly tilted plane, some
surveyors will verify that the vertical control has low residuals and is accurate using multiple vertical control points,
then turn off all but one (V=Off) and use only the nearest vertical (elevation) as they progress through the job.
Note:
The Scale Factor chosen in UNITS under Job Settings will cause all GPS measurements to be adjusted by
the scale factor. For GPS, scale factors can only be entered for one-point localizations (base or rover). For
multi-point rover localizations, the scale factor is computed by the localization and fixed. It appears grayed out
under UNITS in Job Settings. When a scale factor is used for one-point localizations, scaling occurs along the
vector outward from the single localization point in the direction of the measured point. For GPS, the scale factor
acts as a divisor. A scale factor of 0.9 will calculate the measured point 1/0.9 units further away from the single
localization point. Therefore, it is recommended that you keep the scale factor set to 1.0. When configured to total
station, the scale factor is sometimes used to go “ground to grid”. When configured to GPS, the scale factor in is
sometimes used to go “grid to ground”, to better match total station scaling. The scale factor is defined as “ground
to grid”. To go “ground to grid” from high elevations, for example, it would be less than 1. It would multiply total
station measurements and reduce them to grid. It would divide GPS measurements and expand them to ground. If