On March 12th and 13th, 2001, I went around Denver doing stakeout to NGS control stations and recording my occupation position differences. I used the Sprint PCS system (the cell service must have web capability) and the Motorola Timeport phones. This is the way to do RTK in radio congested urban areas! Point PEŅA was 25.75 kilometers (16 miles) from my BASE (in my backyard) and I was within 2 centimeters. My farthest point was HIDDEN at 28.25 kilometers (17.5 miles).
BASE was a nail in my backyard which I positioned from four CORS sites using a 3-hour data set. This position was adjusted vertically, after the fact, by 9 centimeters by holding the known control positions and readjusting BASE. The horizontal change was insignificant. The secret to doing any RTK is to have a good position for your base. Not only coordinate wise, but also physically. My base was weak in both cell strength (barely two bars) and open-sky. At times I had 8 satellites at the rover but was only able to use 6 because of my base location. Some points that I tried to get were not possible because of cell coverage...but I essentially was able to survey all over the city of Denver from one base. Over 200 miles of driving in two days. That's what I call RTK.
After positioning BASE, I went on the NGS website and did a search for all GPS usable control within a 20 mile radius. I got around 90 stations (139 printed pages), some of which I didn't include because of obvious access problems. I entered 84 of them into MapSource for uploading to my Garmin Emap. I also created a text file to upload to Street Atlas just to see if I could do it. I didn't use my laptop with Street Atlas for navigation, because it is easier to do it with the Emap.
Armed with waypoints in my Emap, I set off on my adventure...The first point I went to was TRICE. I couldn't get cell connection there, so I went to MILANO. As I stopped on the road next to the monument, the Emap told me the monument (across the ditch) was 14.9 feet away...gotta love this technology.
This was not a rigorous test for accuracy, just seeing how well the cell phones perform around Denver, and as I stated earlier, I adjusted the elevation of BASE by 0.09 meters after holding the measured control stations (If your going to check control, always start with a good base position). There isn't any Cut/Fill for the first three stations because I wasn't looking at it at first. I'd like to repeat this using one of the control stations as the base, and taking a more methodical approach to recording the data....in any case this is definitely something the urban RTK surveyor needs to look into.
Here are the results as hand recorded:
Station Date Time SV's QC In/Out Lt/Rt Cut/Fill Adj.C/F KM Miles
Milano 12-Mar 10:25 6 0.04 0.06 -0.07 19.62 12.19
Waterman 12-Mar 11:35 5 0.12 0.02 0.03 22.70 14.10
N393 12-Mar 12:15 6 0.04 0.02 0.02 22.80 14.16
Chase 12-Mar 13:20 6 0.05 -0.02 0.03 0.01 -0.08 17.85 11.09
Copp 12-Mar 14:25 6 0.03 -0.03 0 0.05 -0.04 13.12 8.15
P409 12-Mar 15:10 6 0.02 -0.02 -0.02 0.18 0.09 13.54 8.41
Larry 12-Mar 16:00 6 0.02 0 -0.02 0.06 -0.03 13.03 8.09
Alameda 12-Mar 16:40 7 0.10 -0.04 0 -0.01 -0.10 18.41 11.43
P409 13-Mar 10:10 7 0.01 0 0 0.12 0.03 13.54 8.41
Hidden 13-Mar 11:10 5 0.13 -0.03 0.01 0.08 -0.01 28.26 17.55
11:35 5 0.05 0 -0.01 0.05 -0.04 28.26 17.55
Pena 13-Mar 2:10 6 0.07 0.01 -0.03 0.07 -0.02 25.79 16.02
2:20 6 0.03 -0.02 -0.01 0.07 -0.02 25.79 16.02
Center 13-Mar 3:20 6 0.05 0.01 -0.02 0.06 -0.03 18.52 11.50
Control entered into Mapsource for uploading to
Garmin Emap.
Ellis R. Veatch II,
PS
Regional GPS Specialist
7882 S. Garfield Way
Centennial, CO 80122
303-917-3608
ellis.veatch@leicaus.com
E-Mail:
ellisv@ellisv.com
URL: http://www.ellisv.com