ALTA Seminar Featuring COLUMBUS

Presented January 16, 2009
ISPLS Convention in Indianapolis, IN

Sideshots and Relative Positional Accuracy (RPA)

During my visit to Indianapolis, several people asked me about sideshots and RPA. While sideshots can be used in the computation of RPA, the computed coordinate position of these points might be close to their true value or very far off the mark (due to a blunder). The coordinate difference errors (between each station pair) could be much larger than the uncertainty computed during a minimally-constrained network adjustment. With no independent check on sideshots, a small relative error ellipse (and passable ALTA test) may give the surveyor an overly-optimistic assessment of their work.
                - Scott Wallace, Chief Technology Officer (January 2009)

ALTA Presentation (PDF format)

Sample project files

After opening the first project (any shown below), enter the Options - Library Manager and select COLUMBUS Initial Options as the active Options Set. Click OK, enter the Options - Units dialog and change the linear units to U.S. Feet. All projects used in this presentation are based on U.S. feet.

Level Network - Two Stations (page 12-21)

Error Propagation (page 31)

Terrestrial Network - 250' x 250' (page 32)

Terrestrial Network - 250' x 250' With Sideshots (page 32)

GPS Network - 250' x 250' (page 33)

GPS Network - 5000' x 5000' (page 34)

Trilateration Network (page 35)

Triangulation Network (page 36)

Triangulation + Trilateration Network (page 37)

Network Design - No Obs Added Yet (page 38-39)

Network Design - With Obs Added (page 38-39)