Spectra Precision Survey Pro v4.6 Ranger User Manual - Manual (Page 119)

Mapping Plane Scale Factor
109
R+h
Radius of
Ellipsoid, R
Ellipsoid
Height, h
Distance on
Ground
Distance on
Ellipsoid
dist
ground
/(R+h) = dist
elip
/R
dist
elip
/dist
ground
= R/(R+h)
k
elip
= R/ (R+h)
In most situations, the ellipsoid scale factor can be calculated at a
single reference elevation and used for the entire survey, but on
surveys where the elevation varies by more than 100 meters, you may
also want to apply a sea level correction. A sea level correction works
by computing a new ellipsoid height for each shot from the average
elevation of the total station and the target.
Combined Scale Factor
Generally, the two scale factors are multiplied together into a
combined scale factor. The combined scale factor is then applied to
grid distances to get ground distances:
k
cf
= k
elip
* k
map
dist
grid
= dist
ground
* k
cf
Survey Pro allows you to scale the measurements you take on the
ground so they properly align with the map grid you are using. This
is set up using the Scale Factor wizard.
Fig. 5: Ellipsoid Scale Factor
The effect of height above the ellipsoid on scale.