So what information comes out of these ODOT garages, the geoid information? Their devices get GPS and with the x, y the ODOT gives them the z?
Josh Luthman Office: 937-552-2340 Direct: 937-552-2343 1100 Wayne St Suite 1337 Troy, OH 45373 On Wed, May 6, 2020 at 2:17 PM Brian Webster <i...@wirelessmapping.com> wrote: > Josh those reference stations are not broadcasting any differential > correction data or anything related to the GPS system. They are physical > reference stations that are precision surveyed and they have a GPS receiver > for referencing the error of the GPS signals compared to their known > physical location. Most are not on towers. Here is NY the bulk of the > stations are located at various DOT offices/Garages. When you are linking > to those for reference it’s a data IP connection, the only RF getting used > is if you use your cell phone to connect to the internet. > > > > Any GPS base stations used for projects are usually Tripod mounted and > data linked in to this reference system. They are broadcasting only a small > footprint to the various GPS devices within a small radius. The portable > base transmitters are usually either UHF low power (4 watts with a rubber > duck antenna) or 900 MHz band. The 900 is more common because they don’t > need a license. The UHF units are supposed to be licensed with the FCC. > > > > Thank you, > > Brian Webster > > www.wirelessmapping.com > > > > *From:* AF [mailto:af-boun...@af.afmug.com] *On Behalf Of *Josh Luthman > *Sent:* Wednesday, May 6, 2020 1:42 PM > *To:* AnimalFarm Microwave Users Group > *Subject:* Re: [AFMUG] Elevation question > > > > Well that's pretty neat! I like how they jump right over our county. I > know their garage has a big tower, always assumed it was for their internal > communication - guess it looks more like that. > > > > > http://www.dot.state.oh.us/Divisions/Engineering/CaddMapping/Aerial/Pages/VRSRTK.aspx > > > > > Josh Luthman > Office: 937-552-2340 > Direct: 937-552-2343 > 1100 Wayne St > Suite 1337 > Troy, OH 45373 > > > > > > On Wed, May 6, 2020 at 11:58 AM Mark Radabaugh <m...@amplex.net> wrote: > > Josh, > > In Ohio ODOT has a statewide RTK system set up that you can get free > access too. It’s accessible over the internet so as long as your GPS > receiver can connect to your phone to make the data connection to the state > RTK system you can use the data. > > ODOT built if for their own use but make it available to the public to > use. I believe in some locations they will set up a 900Mhz or similar > repeater system to broadcast the data but most of the time they just use > cellular data links. > > Mark > > > On May 6, 2020, at 11:37 AM, Brian Webster <i...@wirelessmapping.com> > wrote: > > > > https://en.wikipedia.org/wiki/Real-time_kinematic > > > > Real-time kinematic (RTK) positioning is a satellite navigation > technique used to enhance the precision of position data derived from > satellite-based positioning systems (global navigation satellite systems, > GNSS) such as GPS, GLONASS, Galileo, NavIC and BeiDou. It uses measurements > of the phase of the signal's carrier wave in addition to the information > content of the signal and relies on a single reference station or > interpolated virtual station to provide real-time corrections, providing up > to centimetre-level accuracy.[1] With reference to GPS in particular, the > system is commonly referred to as carrier-phase enhancement, or CPGPS.[2] > It has applications in land survey, hydrographic survey, and in unmanned > aerial vehicle navigation. > > > > > > > > Thank you, > > Brian Webster > > www.wirelessmapping.com > > > > From: AF [mailto:af-boun...@af.afmug.com] On Behalf Of Brian Webster > > Sent: Wednesday, May 6, 2020 11:33 AM > > To: 'AnimalFarm Microwave Users Group' > > Subject: Re: [AFMUG] Elevation question > > > > 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 > > > > 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> > 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 > > > > From: AF [mailto:af-boun...@af.afmug.com] On Behalf Of ch...@wbmfg.com > > Sent: Tuesday, May 5, 2020 2:12 PM > > To: 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 > > 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 > > > -- > AF mailing list > 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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