Oct 2003

Q: No question here, just an old letter from a satisfied OPUS user.

A:

I would like to let you know how much your OPUS program helped me (us) out on a recent Aerial Photo project.

I work for the Sherburne County (Minnesota) Public Works Department. Back in April of this year our department got funding approved to get Digital Orthophotography of the county. It was my task to "survey" in a network of control panel points for the project. I had one survey technician, two trucks and two Trimble 4800 GPS receivers allotted to me to use everyday. I also had access to one of our road survey crew's Trimble 4800's (when they weren't using it!) and I could "borrow" one of our mapping technicians= if I really needed to.20

We had to survey in 26 control points for the project. Fifteen coordinates= would be delivered to the contractor and 11 (check points) would be held back to compare the contractor's final results to and verify the accuracy of the data we were getting. After getting the "X"'s painted on the points we had two weeks to finish the survey. Being that the contractor specified that the control not be done using RTK GPS methods we had to GPS the positions using static methods. I had post processed GPS data in the past using single frequency receivers and new that not having properly trained personnel running the GPS receivers and logging the correct data of each session of the network could result in a lot of headaches for me when I would be post processing the data. Not being able to use the third receiver every day pretty much ruled out trying to do a traditional network survey of our own. Also, all but three of the points were on roads and we would need proper safety equipment (signs, cones etc..) to be in place while we were surveying.

I heard of the OPUS program about a year or so ago at some of our MNDOT Surveying/Engineering seminars from some of the NGS advisors and thought it sounded pretty slick. On occasion when the survey crew was doing a RTK survey and the base receiver was set up on a control point for a few hours I would download the data and send it in to OPUS to see how it compared. It worked very well. After reading up more about the OPUS program on your website I decided to use OPUS to do the survey. I emailed OPUS with a few questions on the antenna height measurement (ARP) value. I received a return email from a very helpful reply which clarified the antenna height to be entered before uploading the data. We were going to run four hour sessions on each point to be sure we had enough data to get a good result both horizontally and vertically. There were a few sceptics when I proposed to them how we should do this job and how long we should run each session. But luckily the County Surveyor and the Public Works Director are very open to using new innovations and techniques. It took a little more than a week (with some overtime) to get all 26 points GPS'd and post processed. It worked very well because each person could run their session(s) independently of the other person(s). Also, I had very little of my own time involved in the post processing. Each day I would try to download the data and by the next morning I had my results (most of the time I would get some of the data back before I had it all sent ). After getting the "final" coordinates on all of the points the project encountered some unforeseen (snow) related delays. I was able to wait until the precise ephemeris data was available and resubmitted the GPS data and came up with a new, more accurate, set of "final" coordinates.= I was hoping to see results of at least <.03m horizontally and <.06m vertically. These precisions were met and easily exceeded! We have recently received the data back on the check points from the contractor. Comparing average values of their solutions for the check points and our surveyed solutions compare quite well (.13m). These exceeded the original goal, set leniently by the County Surveyor, of <.60m.20

Whenever we start a survey now we try to always set our control using the OPUS program. I felt like I needed to thank someone for making this such an enjoyable and seemingly effortless project. The geodetic toolkit is a great help to me(us) and I appreciate the time and effort put into the programs. Thanks again.

(This sounds like an article for some surveying magazine).