Hi Jochen, these are really helpful advices, thank you. I will definitely try the cheapest check with the aluminium foil as soon as I can go to the area ;-), but the base station - rover or separate antenna solution seems to become a solution that needs a bit of testing, will have to apply for the money first.
As for the total station, yes, we are starting from a ground point and create low level ground points walking up the valleys at the moment; but we have to consider measurement errors increasing. Thanks again, I think I got a lot of really useful input, Maria > Am 28.05.2020 um 14:25 schrieb j.hu...@post-ist-da.de: > > Hi Maria, > > the position of the base station at the entrance of the valley sounds > good. Before you invest a lot of money, you could rent a system and try > it out in the field. Most local dealers should have devices available > for rent or tests. > > The problem with wet conditions could have to do with multipathing > effects. Probably a choke ring antenna will be better in these > conditions. You could try an experiment: Put your GPS in a flat box > which is covered with some conductive material (eg aluminium foil) so > that it only "sees" signals from above (the visible sky), not from below > or the lower sides. See if this changes the resulting accuracy. > > Using a GPS antenna mounted on a pole has the advantage that your body > does not obstruct parts of the visible sky. When measuring near a steep > slope, be sure to stand on the side of the slope where the GPS can't > "see" the sky anyway. I know surveyors who use very long poles (like > 3-4m) to position the antenna above the lower layer of vegetation. You > get errors due to the lack of verticality but much better reception. > > You can't expect to get cm accuracy in the conditions you describe, at > least not with short-time measurements. For this you need phase tracking > which is very sensitive even to short obstructions of a satellite signal > (canopy). > > Unfortunately it sound like you don't have sight contact on ground level > either, so a GPS base station as a reference and a total station for > measuring the individual points won't be an option. > > Regards > Jochen > > > > Am 28.05.20 um 01:53 schrieb Priv.-Doz. Dr. Maria Shinoto: >> Hi fellow archaeologists ;-), >> >> there is so much precious information in this thread. >> >> Now one question about precision and accuracy: As I said, we work in a >> densely forested area, there is not just the canopy of the trees, but two to >> three levels below with dense ground cover and bamboo walls. Still, we get >> excellent (precise) results with consumer level handhelds and smartphones. >> But the accuracy is not good under certain conditions: Water and muddy >> ground seems to be an obstacle for GPS as well as the steep slopes. We get >> very precise results in certain places, but they are in certain cases >> several meters apart from the "real" place -- which we can test with the >> LiDAR DTM. Dry underground and measurement about 10m apart from the slopes >> result in accurate positions, but any measurement point closer to the slopes >> leads to a consistent error in the measurement -- across devices. >> >> I still wonder whether these conditions are suitable for any GPS technology >> or whether working with a fixed station and a rover would be OK. I could >> then think of positioning the station at the entrance of the valley and >> walking up narrowing valley with the rover. >> >> Best, >> Maria >> >> >>> Am 28.05.2020 um 02:17 schrieb Nicolas Cadieux >>> <nicolas.cadi...@archeotec.ca>: >>> >>> Hi Garth, >>> >>> I am also an archaeologist. We use a single Sxblue 2 from GENEQ. The unit >>> was upgraded by the company so it’s takes in the Russian constellation now. >>> The unit is very precise. When we go out on the field, we let le unit run >>> one a Bench mark for a few hours. We then process that position In PPP or >>> using nrcan gps tower if we are close to one. The company give a really >>> good service helping with both software support and hardware. As >>> everything in made and designed in Québec, they can take the unit appart >>> and change individual parts and chips. We did that one as the Bluetooth >>> chip was now longer capable of working with Windows 10 (more likely the >>> other way around). It had been Made for Windows 95. For a few extra bucks, >>> they changed the gps chip also. The unit is basically a brick (Square and >>> heavy) that connects to an external device like a laptop or a tablet. No >>> screens or anywhere fancy. >>> >>> https://geneq.com/land-surveying-geomatics/fr/fabricant/sxblue >>> >>> Nicolas Cadieux >>> Ça va bien aller! >>> >>>> Le 27 mai 2020 à 11:19, QGIS.USER <qgis.u...@raycar.plus.com> a écrit : >>>> >>>> Hi Garth, >>>> Thank you for the correction and the additional information. Much >>>> appreciated. >>>> >>>> My current thinking is that in the archaeology we do, the intra-site >>>> (relative) measurements are quite good but what is inaccurate is the >>>> absolute measurements. We can set out our grids with cm accuracy but can >>>> only locate them on the ground with 10s of metre accuracy. It would be >>>> good to have a low cost way of establishing the absolute position even if >>>> that took time and/or was off-line. >>>> >>>> Ray Carpenter, >>>> Chapel Archaeology >>>> >>>> -----Original Message----- >>>> From: Garth Fletcher [mailto:ga...@jacqcad.com] >>>> Sent: 27 May 2020 15:25 >>>> To: QGIS.USER; qgis-user@lists.osgeo.org >>>> Subject: Re: [Qgis-user] wishing for accurate lattitude/longitude from, a >>>> cell phone >>>> >>>> Hi Ray, >>>> >>>> Apologies for the typo - I had typed iGS3, but iG3s is the right number. >>>> >>>> iGage >>>> <https://smex-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=www.igage.com&umid=068947a3-968f-435b-8f88-0b9b8eb439a9&auth=276d51547942e21b974d48c8cd7101aa75dd6e1a-f9ccd777f828c1b394629f942585917bb0a34506> >>>> iG3s, now replaced by the iG4 which adds Galileo >>>> tracking but otherwise seems very similar to the iG3s. $2400 US. >>>> >>>> These track satellites from the US GPS, Russian GLONASS, Chinese BeiDou >>>> and, with the iG4, European Galileo constellations. >>>> >>>> Their sole function is to record from all the satellites they can track. >>>> >>>> They produce a RINEX format file which can be sent to a post processing >>>> service such as Canada's Geodetic Surveys' CSRS-PPP: >>>> <https://webapp.geod.nrcan.gc.ca/geod/tools-outils/ppp.php?locale=en> >>>> >>>> The longer the observation (recording) duration, the better CSRS-PPP can >>>> converge to an accurate location. In my experience in New Hampshire's >>>> heavily wooded environment, a 30 to 45 minute observation time generally >>>> gets me to better than ± 1 meter accuracy. Yesterday a 6 hour long >>>> observation in a small field surrounded by forest converged to within 1 >>>> inch. Dense forest canopy reduces the number of satellites that can be >>>> tracked. Also, some times of day are better than others in terms of the >>>> number of satellites and their geometry, see: >>>> <https://www.gnssplanning.com/#/charts> >>>> >>>> The iG3s was perfect for my specific conditions, but I think it is not >>>> optimal where many locations within a site must be accurately me >>> _______________________________________________ >>> Qgis-user mailing list >>> Qgis-user@lists.osgeo.org >>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user >>> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user >> _______________________________________________ >> Qgis-user mailing list >> Qgis-user@lists.osgeo.org >> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user >> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user > > > _______________________________________________ > Qgis-user mailing list > Qgis-user@lists.osgeo.org > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user _______________________________________________ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
