Learning reliable procedures for effective GPS surveying has taken me nearly as long as paying off my equipment, but with the advent of better software and additional satellites, including GLONASS,  I am beginning to incorporate GPS into almost every survey.  I still rely on total stations for deep canyons and forest ground, but on open sites I can collect boundary and topographic information accurately and efficiently using almost exclusively the GPS..

This month I make the 36'th and last, monthly payment on my Topcon XT and I'm finally starting to love it.  It has been a somewhat stormy relationship, and the equipment is somewhat finicky and tempramental, but I think we are settling down to a long marriage.  The software has improved in the last three years and the XT has finally become a reliable instrument.  In my skinned-down office, I've been doing most of our field work by myself, and I enjoy carrying less and accomplishing more than I could with a two-man total-station crew. GPS also allows the user to collect real-world coordinates for our projects so that I can provide elevation and positional services. More and more I am post-processing the location of my base station and retaining the real-world elevation, latitude and longitude, regardless of whether the job requires this information.

Here is a sort of check-list and procedural run through for effective GPS/Static/RTK data collection and staking, and some helpful hints.

Make sure all batteries are charged,  and collector and receiver memories are clear.

Pre-calculate & upload any local coordinate information needed

At the project site, locate a suitable base station. This is usually the highest point in the project location, with as nearly unobstructed view of the heavens as possible.  The station should also be away from buildings, tall fences or power lines.    Another consideration is site security; I have frequently left the base station unattended in remote areas, but I am nervous about leaving it alone in a high-traffic area.  These units are brightly colored, very portable and very expensive.  In busy sites I like to leave a baby-sitter with the base station.  OPUS currently requires a minimum of two hours to process a solution (15 minutes with rapid static), and still, longer occupations achieve better results.  The base station simultaneously collects location information and transmits correction to the rover.  If I want a check on the observed elevations, I will collect static information at two or more points and then include these stations in a level loop or closed traverse.  That way I am able to compare post-processed elevations with relative elevations.

For RTK, most collectors can vary the elevation mask and the duration of the the observations.  I have not noticed significant increases in accuracy by increasing the observation times.  I seem to achieve higher precision by taking multiple 3 or 5 second observations and averaging the results.  This also allows me to examine and remove any suspicious results.  Changing the elevation mask upwards or downward can sometimes help the rover obtain a fix when satellites are blinking in and out of trees or other objects, or too near the horizon.

Sometimes there are sunspots, or a space storm, or another cosmic mystery and the rover loses a fix; when this happens you need to wait.  The constellation resolves, GPS surveying requires a different kind of patience from traditional surveying, yelling at your chainman won't achieve a satellite fix, and some locations are simply not suitable for GPS.  In this case we will locate two stations where the RTK is reliable and shoot the point is with the total station.

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