[Qgis-user] wishing for accurate lattitude/longitude from, a cell phone

Thu May 28 16:05:35 PDT 2020

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.huber at 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.cadieux at 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.user at 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:garth at jacqcad.com] 
>>>> Sent: 27 May 2020 15:25
>>>> To: QGIS.USER; qgis-user at 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
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