Spectra Precision FAST Survey Reference Manual - Manual (Page 107)

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 C & R (Curvature and Refraction)
: This option applies only to total station configurations and will be
unavailable when your instrument is configured to any GPS option. This factor causes an adjustment in distance
measurement. Effects are negligible except over long distances. It is recommended that this toggle be enabled,
except in those very rare cases where the instrument factors in curvature and refraction.
 Sea Level Correction
: If the sea level correction toggle is enabled (Use Ground to Grid is clicked off), the
horizontal distance at the source point's elevation is reduced to the sea level chord using the mean height of the
vector. Typically this value is negligible unless measuring very long distances.
 Use Ground to Grid (Scale Factor)
: If clicked on (as above), then you can automatically calculate the Ground to
Grid factor. For most applications, the Ground to Grid Scale Factor for total station work should be set to 1.0. This
uses the actual measurements from the total station for all distances. However to convert total station ground
measurements to match GPS measurements, the ground to grid scale factor can be computed (or hand-entered) by
clicking the "Calculate" icon. This leads to the dialog at right. A local coordinate and average height can be
entered or recalled from the list of points or from the map screen. This will compute the grid factor (from the
projection) as well as the elevation factor to produce the combined grid/elevation factor that reduces ground
distances to grid. Therefore, for total stations, the scale factor acts as a multiplier. All distance measurements taken
by a total station will be multiplied by the scale factor. 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.
 Average Icon
: The summation or "averaging" icon at the top of the dialog can be used to get an average height and
coordinate position from a range of points. Here is an example where 5 points were used to create an "average"
combined factor. This feature recognizes the different elevation impacts of metric versus English units. Be sure
that the selected points have correct, non-zero elevations, or scroll right to the V On column and turn Vertical off
for purposes of averaging.
 Calculate:
With Calculate turned on within the "TS Ground to Grid" dialog (at right), the Grid Factor is
automatically multiplied by the Sea Level Factor to produce the Combined Factor. With Calculate turned off, you