I see Trimble has a R1 GNSS receiver model that pairs via bluetooth with your phone/tablet.
1. Are they accurate enough to trust for surveying things like power poles/tower locations. 2. They’re $2500 retail, is there a cheaper option that still has “reasonable” accuracy? My experience with consumer grade GPS units is that they’re frequently inaccurate, sometimes wildly. Makes a difference when you’re near a property line. > On May 6, 2020, at 8:32 AM, Brian Webster <i...@wirelessmapping.com> wrote: > > High end stuff. I never trust any consumer grade GPS device altitude > readings. I have seen them off by as much as 300 to 400 feet. High end GPS > devices rely on either a real time data link to ground reference stations or > they post process the data back at the office. This is a process where you > time sync your data with the ground reference stations, calculate the timing > difference based on your location distance from the ground control points. > The ground control points have a known coordinate and altitude. They then > compare the GPS readings at their point for those time reference points you > process against. They calculate the correction factor from the GPS against > the known point, then also correct your data based on the distance/time from > the ground station and correct your data. For older GPS units you sometimes > had to occupy a point for a longer period of time based on your distances > from the control points. > > High end GPS units can also do RTK or real time kinematic data collection. > This is done by either having a GPS base station controller that is real time > data linked to ground control stations or that the rover unit has the real > time data connectivity. They do all the above processing steps in real time, > no post processing after the field work is done. Depending on the equipment > and setup, there are time requirements to have the instrument on point to > achieve the desired level of precision. Depending on the type of work, faster > systems are desired when you are doing things like having to stand in traffic > to map every manhole and gas valve. Other uses that are slower can be fine if > you can leave it on a tri-pod or bi-pod for 30 seconds or longer. Slower > systems are preferred by workers getting paid prevailing wages ;-) > > > Thank you, > Brian Webster > www.wirelessmapping.com <http://www.wirelessmapping.com/> > > From: AF [mailto:af-boun...@af.afmug.com] On Behalf Of Josh Luthman > Sent: Wednesday, May 6, 2020 11:17 AM > To: AnimalFarm Microwave Users Group > Subject: Re: [AFMUG] Elevation question > > >local Geoid data set loaded > > Is this something most GPS radios would have? Or just higher end ones? > > Josh Luthman > Office: 937-552-2340 > Direct: 937-552-2343 > 1100 Wayne St > Suite 1337 > Troy, OH 45373 > > > On Wed, May 6, 2020 at 10:36 AM Brian Webster <i...@wirelessmapping.com > <mailto:i...@wirelessmapping.com>> wrote: >> OK here is what I learned from my brother. >> >> You want to use the Geoid values, however you also want to make sure you >> have the Geoid model loaded in to your Trimble R8 GPS. (for those not paying >> attention that is a survey grade instrument with cm accuracy). >> The geoid numbers are tied to the map projection you are using and they are >> also tied to the GPS ground stations you are connected to 9necessary for the >> cm grade accuracy). The Ellipsoid values assume that the earth is >> perfectly/mathematically round. Geoid values correct for the fact that it is >> not perfectly round and the reason why your GPS needs the local Geoid data >> set loaded before you take readings. You do have the Geoid data for your >> area loaded don’t you? >> >> For radio mobile you will want to use the Geoid height converted to meters. >> >> Is there LIDAR data for the area in question? It might be easier just to use >> a value from that. Might also be nice to convert the LIDAR to a file format >> for Radio Mobile and use all that data (going to need a lot of disk space >> though). >> >> Thank you, >> Brian Webster >> www.wirelessmapping.com <http://www.wirelessmapping.com/> >> >> From: AF [mailto:af-boun...@af.afmug.com <mailto:af-boun...@af.afmug.com>] >> On Behalf Of ch...@wbmfg.com <mailto:ch...@wbmfg.com> >> Sent: Tuesday, May 5, 2020 2:12 PM >> To: af@af.afmug.com <mailto:af@af.afmug.com> >> Subject: [AFMUG] Elevation question >> >> I have a pretty good GPS receiver. Trimble R8 with a Yuma data collector. >> Normally we use it only for lats and longs. >> It is corrected in real time with a cellular data modem and a RTK/VRS ground >> station network. >> >> Yesterday we did a shot from a hill that did not exist when shuttle radar >> data was taken. It was way off in elevation. >> So we took a shot from our parking lot and compared it with what we think we >> know to be the altitude as well as our cell phones and google earth. >> >> Turns out the R8 has an ellipsoid height as well as another height >> associated with the northing and easting values. >> The second one seems to be more in line with what I was expecting. >> The local dealer sent me a drawing showing this. (attached) >> >> So now I am super confused. Not sure what number to use when working with >> Radio Mobile. Do I add the geoid height to the ellipsoid height? >> >> Was hoping Brian Webster may know or others may know. Googling google earth >> elevation talks about different versions of geoid. Not sure if their >> elevations are geoid elevations or not. >> >> So, rather than dig into it any more I am taking the lazy approach and >> posting the question here. >> -- >> AF mailing list >> AF@af.afmug.com <mailto:AF@af.afmug.com> >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >> <http://af.afmug.com/mailman/listinfo/af_af.afmug.com>-- > AF mailing list > AF@af.afmug.com > http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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