I have 5+ years running Topcon Hipers with a traditional base and rover setup and became very comfortable with what to expect from the system for elevations. Over the last year I've rented the Spectra Precision Epoch 35 system a number of times, setup as a network rover utilizing the Ohio ODOT VRS network and have noticed some alarming results with elevations. Most of the time when shots were compared to existing control or existing shots from my robot the results were very close, but other times the elevations and/ or horizontal coordinates would be come very sloppy for no apparent reason. For the most part these "sloppy shots" resulted when there was a small amount of blockage of the horizon on one side, but nothing that seemed unreasonable. The part that was alarming to me is the system never seems to go into float or start to report horz. or vert. residuals above .08'. Now I know just because the data collector says "fixed" it doesn't that I can start taking shots anywhere I please. I was just used to more sensitivity when it came to the Hiper Base/Rover reporting a "float" solution or the higher residuals when the number or geometry of the satellites was unfavorable. I did some searching around for information on this subject and did run into sum articles about achieving better results from a rover/ base setup due to the distance between the two and observing the same satellites. Can somebody educate me on this as I thought the network rover was going to be my next purchase, but now I'm not sure about it.
Kelly Dunford
My experience with VRS is the same.
I do not like them, (yet) too sloppy.
🙁
some (heavy) recommended reading
Department of Natural Resources Management and
Engineering
NRME Monographs
University of Connecticut Year 2007
What Does Height Really Mean?
Thomas H. Meyer Daniel R. Romany
David B. Zilkoski
ln58 from ngs
GUIDE TO GPS
POSITIONING
DAVID WELLS
NORMAN BECK
DEMITRIS DELIKARAOGLOU
ALFRED KLEUSBERG
EDWARD J. KRAKIWSKY
GERARD LACHAPELLE
RICHARD B. LANGLEY
METE NAKIBOGLU
KLAUS-PETER SCHWARZ
JAMES M. TRANQUILLA
PETR VANICEK
November 1999
JOURNAL OF SURVEYING ENGINEERING © ASCE / MAY 2010 / 91
OPUS-RS Pair Points: Case Study
Peter Lazio, PLS, M.ASCE1
NOAA Technical Memorandum NOS NGS 59
Guidelines for Establishing GPS-Derived
Orthometric Heights
David B. Zilkoski
Edward E. Carlson
Curtis L. Smith
i asked him for a copy. he kindly sent me one.
ftp://ftp.ngs.noaa.gov/dist/whenning/RT21May09/
http://www.ngs.noaa.gov/corbin/class_description/RTK.shtml
ftp://ftp.ngs.noaa.gov/pub/corbin/RTK Webinar/
ftp://ftp.ngs.noaa.gov/dist/whenning/RT21May09/
some (heavy) recommended reading
None of your links work.
You haven't told us really anything about your procedures when doing RTK... so read this and tell us what you are doing compared to it:
http://www.ngs.noaa.gov/PUBS_LIB/NGSRealTimeUserGuidelines.v1.1.pdf
Yeah and I know the NGS guide is tailored to a single baseline solution instead of a network one, but that is okay. Still tell us about your procedures vs what NGS says you should be doing for the accuracy you are looking for.
I don't trust the VRS stuff for elevations (Trimble's Network)...I have seen fluctuations up to 0.3'...however, the horizontals of my VRS almost always are within a tenth, compared to a conventional base/rover RTK stuff.
The horizontal distances are generally close enough for my purposes.
Yeah, I can live with a 0.1' horizontally, it's the 0.3' plus vertically that is more than what I'm used to dealing with from RTK. I've often had spreads in the .25' range from RTK, but it also reported high residuals and a low number of satellites. The network receiver showed a high number of satellites and low residuals all day long.
I recently purchased an Epoch 35 in December. We use it on the NC VRS network and have had favorable results when setting grid control. Most instances we'll be under .02' H and .04 V positionally and exceed 95% confidence. Being in the mountains I don't have many oportunities to use it for regular topo and locations, mainly just setting Grid control. When I've had unfavorable data it's usually due to multipath/geometry/poor cell service. When setting control we try to do some planning on the front end so that we will be collecting data at an optimum time. That said, when occupying these points with the robot we've had the horizontal/vertical check very well---better than the positional accuracy calculator shows (if you don't have a positional accuracy calculator, contact Clay @ Duncan-Parnell). Not sure if this helps, just my experience so far.
Wes Cole
I will have to ask Clay about this calculator....
Okay, I'll probably get flamed for this one, but what is a positional accuracy calculator?
Is it equipment specific?
some (heavy) recommended reading
> None of your links work."
OK, so they don't. if you want to read them badly enough, try the ngs publications:
http://www.ngs.noaa.gov/PUBS_LIB/pub_index.shtml
much of what i posted above is there. anything else, let me know, i will try another way to get it to you
Can you do a short static session on critical points to give yourself some extra confidence?
Have you tried observing the same point at varying times with varying satellite geometry?
