Re: [Qgis-user] Tablet vs GPS accuracy
I´ve just been introduced to this solutions - might be of interest: http://swift-nav.com/piksi.html Lene Fischer Associate Professor Department of Geosciences and Natural Resource Management University of Copenhagen MOB +45 40115084 l...@ign.ku.dkmailto:l...@ign.ku.dk [SCIENCE_bomaerke_UK] Fra: qgis-user-boun...@lists.osgeo.org [mailto:qgis-user-boun...@lists.osgeo.org] På vegne af Lene Fischer Sendt: 10. april 2014 08:23 Til: Bo Victor Thomsen; qgis-user@lists.osgeo.org Emne: Re: [Qgis-user] Tablet vs GPS accuracy I´ve been looking to the issue using an Android for collecting GPS data. Try to look at RTKlib http://www.rtklib.com/ An OpenSource program - might give inspiration. And also this note http://www.diydrones.com/profiles/blogs/rtk-lib-ported-to-android Regards Lene Fischer From: qgis-user-boun...@lists.osgeo.orgmailto:qgis-user-boun...@lists.osgeo.org [qgis-user-boun...@lists.osgeo.org] on behalf of Bo Victor Thomsen [bo.victor.thom...@gmail.com] Sent: 04 April 2014 10:32 To: qgis-user@lists.osgeo.orgmailto:qgis-user@lists.osgeo.org Subject: Re: [Qgis-user] Tablet vs GPS accuracy If you are working with tablets and an external GPS connected to the tablet using USB or Bluetooth, you should have a look at some of the new GNSS mouse type GNSS - receivers that support both both GPS and GLONASS. The are significantly more accurate and positionally stable than the GPS only types (in the same price range). I have used a HOLUX M-215+ (remember the + - it means GLONASS compatibility) and have a accuracy around 1 meter in the open land most of the time. The HOLUX unit cost around 60 Euros. Regards Bo Victor Thomsen Aestas-GIS Denmark Den 04-04-2014 04:32, Leo Kris Palao skrev: Hi Guys, Thanks all for your valuable insights about my inquiry. I really appreciate your comments. I can use your comments as reference on how we will also evaluate GIS applications in Tablets. Our application mainly falls on agriculture. We want to use the tablets for surveying in Rural areas. And we want to use QGIS android so we can load our shapefile and raster maps for validation. On the other hand, we will also want to use tablets to take location of field corners of farmers field to get the plot size (this is where accuracy is important). I observe that when there is a wifi the location significantly increases in tablets. But of course, wifi is not available in rural areas. So, if we will use tablet we will just rely on available GPS signal, weather, and the device. Thank so much, and again I really appreciate the comments, -Leo On Fri, Apr 4, 2014 at 2:20 AM, Michael.Dodd michael.d...@open.ac.ukmailto:michael.d...@open.ac.uk wrote: I agree with the points Richard has made here. I mentioned in an earlier message on this topic that I'd done a lot of testing with smartphones vs consumer gps see http://www.open.ac.uk/blogs/otih/?p=466 for details on some of the tests. Also tested consumer grade gps and a range of other surveying techniques with results and discussion shown here: http://oro.open.ac.uk/30066/ From: Richard McDonnell [richard.mcdonn...@opw.iemailto:richard.mcdonn...@opw.ie] Sent: Thursday, April 03, 2014 4:09 PM To: Leo Kris Palao Cc: QGIS Mailing List Subject: Re: [Qgis-user] Tablet vs GPS accuracy Hi, It all boils down to the level of accuracy your job requires, Commercial or Survey Grade GNSS (Global Navigation Satellite System) now utilises NRTK (Network Real Time Kinematic) which can produce sub centimetre accuracies. We have found that the accuracies is often too good, with our surveys conflicting with Maps. We have seen +-40mm accuracies in the field, where a stake in the ground is surveyed and the kit can take us right back to the point days later, to within 40mm. it is worth noting that Survey grade GPS has a stated accuracy of sub meter without NRTK. The next step down in accuracies would be GPS enabled Field Computers, again a dedicated kit but hand held form factor, the Trimble Geo-Explorer 7 is an example of one of these. They now also have the ability to utilise NRTK, bringing there accuracies to within 0.5m (or better). The issue with phones and tablets is that, unlike dedicated systems, you have less control over how the coordinates are recorded. They don't take into account things like multipath (GPS signal bouncing off buildings, Ground etc.) The number of satellites (the more the better) Most survey kits wont record a point with less than 5 satellites. There is a way to get an idea of the accuracy for your proposed device. Take several readings over a day (7 or more) of 2 fixed points approx 50m apart, every day, for a week. Then compare the results. you will have a spread of points, none of which are likely to be perfect, but will give you an idea of the accuracies of the device, the spread of the points being your expected error. A shorter test over
Re: [Qgis-user] Tablet vs GPS accuracy
Another low cost RTK solution: http://www.emlid.com/ Some test results are available here:http://www.diydrones.com/profiles/blogs/navio-rtk-demonstration Kris Gesendet:Donnerstag, 24. April 2014 um 11:40 Uhr Von:Lene Fischer l...@ign.ku.dk An:qgis-user@lists.osgeo.org qgis-user@lists.osgeo.org Betreff:Re: [Qgis-user] Tablet vs GPS accuracy Ive just been introduced to this solutions might be of interest: http://swift-nav.com/piksi.html Lene Fischer Associate Professor Department of Geosciences and Natural Resource Management University of Copenhagen MOB +45 40115084 l...@ign.ku.dk Fra: qgis-user-boun...@lists.osgeo.org [mailto:qgis-user-boun...@lists.osgeo.org] P vegne af Lene Fischer Sendt: 10. april 2014 08:23 Til: Bo Victor Thomsen; qgis-user@lists.osgeo.org Emne: Re: [Qgis-user] Tablet vs GPS accuracy Ive been looking to the issue using an Android for collecting GPS data. Try to look at RTKlibhttp://www.rtklib.com/ An OpenSource program - might give inspiration. And also this notehttp://www.diydrones.com/profiles/blogs/rtk-lib-ported-to-android Regards Lene Fischer From: qgis-user-boun...@lists.osgeo.org [qgis-user-boun...@lists.osgeo.org] on behalf of Bo Victor Thomsen [bo.victor.thom...@gmail.com] Sent: 04 April 2014 10:32 To: qgis-user@lists.osgeo.org Subject: Re: [Qgis-user] Tablet vs GPS accuracy If you are working with tablets and an external GPS connected to the tablet using USB or Bluetooth, you should have a look at some of the new GNSS mouse type GNSS - receivers that support both both GPS and GLONASS. The are significantly more accurate and positionally stable than the GPS only types (in the same price range). I have used a HOLUX M-215+ (remember the + - it means GLONASS compatibility) and have a accuracy around 1 meter in the open land most of the time. The HOLUX unit cost around 60 Euros. Regards Bo Victor Thomsen Aestas-GIS Denmark Den 04-04-2014 04:32, Leo Kris Palao skrev: Hi Guys, Thanks all for your valuable insights about my inquiry. I really appreciate your comments. I can use your comments as reference on how we will also evaluate GIS applications in Tablets. Our application mainly falls on agriculture. We want to use the tablets for surveying in Rural areas. And we want to use QGIS android so we can load our shapefile and raster maps for validation. On the other hand, we will also want to use tablets to take location of field corners of farmers field to get the plot size (this is where accuracy is important). I observe that when there is a wifi the location significantly increases in tablets. But of course, wifi is not available in rural areas. So, if we will use tablet we will just rely on available GPS signal, weather, and the device. Thank so much, and again I really appreciate the comments, -Leo On Fri, Apr 4, 2014 at 2:20 AM, Michael.Dodd michael.d...@open.ac.uk wrote: I agree with the points Richard has made here. I mentioned in an earlier message on this topic that Id done a lot of testing with smartphones vs consumer gps see http://www.open.ac.uk/blogs/otih/?p=466 for details on some of the tests. Also tested consumer grade gps and a range of other surveying techniques with results and discussion shown here: http://oro.open.ac.uk/30066/ From: Richard McDonnell [richard.mcdonn...@opw.ie] Sent: Thursday, April 03, 2014 4:09 PM To: Leo Kris Palao Cc: QGIS Mailing List Subject: Re: [Qgis-user] Tablet vs GPS accuracy Hi, It all boils down to the level of accuracy your job requires, Commercial or Survey Grade GNSS (Global Navigation Satellite System) now utilises NRTK (Network Real Time Kinematic) which can produce sub centimetre accuracies. We have found that the accuracies is often too good, with our surveys conflicting with Maps. We have seen +-40mm accuracies in the field, where a stake in the ground is surveyed and the kit can take us right back to the point days later, to within 40mm. it is worth noting that Survey grade GPS has a stated accuracy of sub meter without NRTK. The next step down in accuracies would be GPS enabled Field Computers, again a dedicated kit but hand held form factor, the Trimble Geo-Explorer 7 is an example of one of these. They now also have the ability to utilise NRTK, bringing there accuracies to within 0.5m (or better). The issue with phones and tablets is that, unlike dedicated systems, you have less control over how the coordinates are recorded. They dont take into account things like multipath (GPS signal bouncing off buildings, Ground etc.) The number of satellites (the more the better) Most survey kits wont record a point with less than 5 satellites. There is a way to get an idea of the accuracy for your proposed device. Take several readings over a day (7 or more) of 2 fixed points approx 50m apart, every day, for a week
Re: [Qgis-user] Tablet vs GPS accuracy
I´ve been looking to the issue using an Android for collecting GPS data. Try to look at RTKlib http://www.rtklib.com/ An OpenSource program - might give inspiration. And also this note http://www.diydrones.com/profiles/blogs/rtk-lib-ported-to-android Regards Lene Fischer From: qgis-user-boun...@lists.osgeo.org [qgis-user-boun...@lists.osgeo.org] on behalf of Bo Victor Thomsen [bo.victor.thom...@gmail.com] Sent: 04 April 2014 10:32 To: qgis-user@lists.osgeo.org Subject: Re: [Qgis-user] Tablet vs GPS accuracy If you are working with tablets and an external GPS connected to the tablet using USB or Bluetooth, you should have a look at some of the new GNSS mouse type GNSS - receivers that support both both GPS and GLONASS. The are significantly more accurate and positionally stable than the GPS only types (in the same price range). I have used a HOLUX M-215+ (remember the + - it means GLONASS compatibility) and have a accuracy around 1 meter in the open land most of the time. The HOLUX unit cost around 60 Euros. Regards Bo Victor Thomsen Aestas-GIS Denmark Den 04-04-2014 04:32, Leo Kris Palao skrev: Hi Guys, Thanks all for your valuable insights about my inquiry. I really appreciate your comments. I can use your comments as reference on how we will also evaluate GIS applications in Tablets. Our application mainly falls on agriculture. We want to use the tablets for surveying in Rural areas. And we want to use QGIS android so we can load our shapefile and raster maps for validation. On the other hand, we will also want to use tablets to take location of field corners of farmers field to get the plot size (this is where accuracy is important). I observe that when there is a wifi the location significantly increases in tablets. But of course, wifi is not available in rural areas. So, if we will use tablet we will just rely on available GPS signal, weather, and the device. Thank so much, and again I really appreciate the comments, -Leo On Fri, Apr 4, 2014 at 2:20 AM, Michael.Dodd michael.d...@open.ac.ukmailto:michael.d...@open.ac.uk wrote: I agree with the points Richard has made here. I mentioned in an earlier message on this topic that I'd done a lot of testing with smartphones vs consumer gps see http://www.open.ac.uk/blogs/otih/?p=466 for details on some of the tests. Also tested consumer grade gps and a range of other surveying techniques with results and discussion shown here: http://oro.open.ac.uk/30066/ From: Richard McDonnell [richard.mcdonn...@opw.iemailto:richard.mcdonn...@opw.ie] Sent: Thursday, April 03, 2014 4:09 PM To: Leo Kris Palao Cc: QGIS Mailing List Subject: Re: [Qgis-user] Tablet vs GPS accuracy Hi, It all boils down to the level of accuracy your job requires, Commercial or Survey Grade GNSS (Global Navigation Satellite System) now utilises NRTK (Network Real Time Kinematic) which can produce sub centimetre accuracies. We have found that the accuracies is often too good, with our surveys conflicting with Maps. We have seen +-40mm accuracies in the field, where a stake in the ground is surveyed and the kit can take us right back to the point days later, to within 40mm. it is worth noting that Survey grade GPS has a stated accuracy of sub meter without NRTK. The next step down in accuracies would be GPS enabled Field Computers, again a dedicated kit but hand held form factor, the Trimble Geo-Explorer 7 is an example of one of these. They now also have the ability to utilise NRTK, bringing there accuracies to within 0.5m (or better). The issue with phones and tablets is that, unlike dedicated systems, you have less control over how the coordinates are recorded. They don't take into account things like multipath (GPS signal bouncing off buildings, Ground etc.) The number of satellites (the more the better) Most survey kits wont record a point with less than 5 satellites. There is a way to get an idea of the accuracy for your proposed device. Take several readings over a day (7 or more) of 2 fixed points approx 50m apart, every day, for a week. Then compare the results. you will have a spread of points, none of which are likely to be perfect, but will give you an idea of the accuracies of the device, the spread of the points being your expected error. A shorter test over a day would yield similar results but over a week, you would have a more comprehensive result. I have seen some tests, where accuracies with an i-Phone were stated as +-3m. One other thing you should all note when using a phone or similar device to record your location, Use the native Latitude and Longitude to record the position, don't use the device to transform the coordinates to some other CRS. Use a dedicated CRS Transformation tool on a desktop/Laptop computer to convert to your desired CRS. Handhelds are not suitable for that purpose. I hope this helps!! Regards, Richard. On 03/04
Re: [Qgis-user] Tablet vs GPS accuracy
If you are working with tablets and an external GPS connected to the tablet using USB or Bluetooth, you should have a look at some of the new GNSS mouse type GNSS - receivers that support both both GPS and GLONASS. The are significantly more accurate and positionally stable than the GPS only types (in the same price range). I have used a HOLUX M-215+ (remember the + - it means GLONASS compatibility) and have a accuracy around 1 meter in the open land most of the time. The HOLUX unit cost around 60 Euros. Regards Bo Victor Thomsen Aestas-GIS Denmark Den 04-04-2014 04:32, Leo Kris Palao skrev: Hi Guys, Thanks all for your valuable insights about my inquiry. I really appreciate your comments. I can use your comments as reference on how we will also evaluate GIS applications in Tablets. Our application mainly falls on agriculture. We want to use the tablets for surveying in Rural areas. And we want to use QGIS android so we can load our shapefile and raster maps for validation. On the other hand, we will also want to use tablets to take location of field corners of farmers field to get the plot size (this is where accuracy is important). I observe that when there is a wifi the location significantly increases in tablets. But of course, wifi is not available in rural areas. So, if we will use tablet we will just rely on available GPS signal, weather, and the device. Thank so much, and again I really appreciate the comments, -Leo On Fri, Apr 4, 2014 at 2:20 AM, Michael.Dodd michael.d...@open.ac.uk mailto:michael.d...@open.ac.uk wrote: I agree with the points Richard has made here. I mentioned in an earlier message on this topic that I'd done a lot of testing with smartphones vs consumer gps see http://www.open.ac.uk/blogs/otih/?p=466 for details on some of the tests. Also tested consumer grade gps and a range of other surveying techniques with results and discussion shown here: http://oro.open.ac.uk/30066/ From: Richard McDonnell [richard.mcdonn...@opw.ie mailto:richard.mcdonn...@opw.ie] Sent: Thursday, April 03, 2014 4:09 PM To: Leo Kris Palao Cc: QGIS Mailing List Subject: Re: [Qgis-user] Tablet vs GPS accuracy Hi, It all boils down to the level of accuracy your job requires, Commercial or Survey Grade GNSS (Global Navigation Satellite System) now utilises NRTK (Network Real Time Kinematic) which can produce sub centimetre accuracies. We have found that the accuracies is often too good, with our surveys conflicting with Maps. We have seen +-40mm accuracies in the field, where a stake in the ground is surveyed and the kit can take us right back to the point days later, to within 40mm. it is worth noting that Survey grade GPS has a stated accuracy of sub meter without NRTK. The next step down in accuracies would be GPS enabled Field Computers, again a dedicated kit but hand held form factor, the Trimble Geo-Explorer 7 is an example of one of these. They now also have the ability to utilise NRTK, bringing there accuracies to within 0.5m (or better). The issue with phones and tablets is that, unlike dedicated systems, you have less control over how the coordinates are recorded. They don't take into account things like multipath (GPS signal bouncing off buildings, Ground etc.) The number of satellites (the more the better) Most survey kits wont record a point with less than 5 satellites. There is a way to get an idea of the accuracy for your proposed device. Take several readings over a day (7 or more) of 2 fixed points approx 50m apart, every day, for a week. Then compare the results. you will have a spread of points, none of which are likely to be perfect, but will give you an idea of the accuracies of the device, the spread of the points being your expected error. A shorter test over a day would yield similar results but over a week, you would have a more comprehensive result. I have seen some tests, where accuracies with an i-Phone were stated as +-3m. One other thing you should all note when using a phone or similar device to record your location, Use the native Latitude and Longitude to record the position, don't use the device to transform the coordinates to some other CRS. Use a dedicated CRS Transformation tool on a desktop/Laptop computer to convert to your desired CRS. Handhelds are not suitable for that purpose. I hope this helps!! Regards, Richard. On 03/04/2014 12:30, Leo Kris Palao wrote: Hi QGIS Users, I would like to inquire if there are some user that already assessed the positioning (location) accuracy of tablet vs commercial gps. We would like to use qgis android for fieldwork. We would also like to try qmap. Thanks, Leo
[Qgis-user] Tablet vs GPS accuracy
Hi QGIS Users, I would like to inquire if there are some user that already assessed the positioning (location) accuracy of tablet vs commercial gps. We would like to use qgis android for fieldwork. We would also like to try qmap. Thanks, Leo ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Tablet vs GPS accuracy
Hi, You will always get better positioning off a commercial GPS than a cellphone based one. I put that in inverted commas because times change, and depending on your terrain (city buildings, trees, mountains) and accuracy requirements, better might not be needed for your job. My suggestion is look at the error ellipse of your device,and decide if it is good enough. If you are positioning doors that are next to each other (like town houses), you need to make sure that the GPS value recorded is close enough to your door, than the one just next to it (like 1.5m away). I used a Garmin 60CSX connected to a QGIS laptop via Franson GPSgate and the solution worked really well. The GPS unit must be capable of streaming NMEA data, so choose carefully. So, with more info about what you want to do, you might get more responses. HTH, Zoltan On 2014/04/03 13:30, Leo Kris Palao wrote: Hi QGIS Users, I would like to inquire if there are some user that already assessed the positioning (location) accuracy of tablet vs commercial gps. We would like to use qgis android for fieldwork. We would also like to try qmap. Thanks, Leo ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user -- === Zoltan Szecsei PrGISc [PGP0031] Geograph (Pty) Ltd. GIS and Photogrammetric Services P.O. Box 7, Muizenberg 7950, South Africa. Mobile: +27-83-6004028 Fax:+27-86-6115323 www.geograph.co.za === ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Tablet vs GPS accuracy
Hei Leo, Unfortunately I do not recall where I read comparison of proper GPS and Smartphones regarding precision. But as far as I remember precision difference depends very much on where you are. Smartphones (and also tablets I guess) make also use of the cell towers / access points to the mobile network for positioning. So, if you are working in towns or populated areas you get probably comparable precision to a commercial GPS (a few meters difference). But if you are in remote areas, difference can be more significant 20m and more... Others please correct me if I am wrong... And as Zoltan writes: what is good (or more precise suitable) depends on your needs... Cheers Stefan ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Tablet vs GPS accuracy
I did a considerable amount of testing comparing conventional gps devices and smartphones and some more advanced gps devices. All compared to cm level dgps locations. One factor to consider is that smartphones tend to be mass produced in much larger numbers than separate gps devices so they can potentially have the latest most accurate chips etc. as far as i recall towers only affect speed of first location not accuracy as the location calculated just from tower is much less accurate than from the gps itself. I also recall reading somewhere that one or two models of smartphone physically have the technology in them to do 0.5m accuracy but this ability is switched off at the moment. From: Blumentrath, Stefan [stefan.blumentr...@nina.no] Sent: Thursday, April 03, 2014 12:59 PM To: Leo Kris Palao; QGIS Mailing List Subject: Re: [Qgis-user] Tablet vs GPS accuracy Hei Leo, Unfortunately I do not recall where I read comparison of “proper GPS” and Smartphones regarding precision. But as far as I remember precision difference depends very much on where you are. Smartphones (and also tablets I guess) make also use of the cell towers / access points to the mobile network for positioning. So, if you are working in towns or populated areas you get probably comparable precision to a commercial GPS (a few meters difference). But if you are in remote areas, difference can be more significant 20m and more… Others please correct me if I am wrong… And as Zoltan writes: what is “good” (or more precise “suitable”) depends on your needs… Cheers Stefan -- The Open University is incorporated by Royal Charter (RC 000391), an exempt charity in England Wales and a charity registered in Scotland (SC 038302). ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Tablet vs GPS accuracy
Hi, It all boils down to the level of accuracy your job requires, Commercial or Survey Grade GNSS (Global Navigation Satellite System) now utilises NRTK (Network Real Time Kinematic) which can produce sub centimetre accuracies. We have found that the accuracies is often too good, with our surveys conflicting with Maps. We have seen +-40mm accuracies in the field, where a stake in the ground is surveyed and the kit can take us right back to the point days later, to within 40mm. it is worth noting that Survey grade GPS has a stated accuracy of sub meter without NRTK. The next step down in accuracies would be GPS enabled Field Computers, again a dedicated kit but hand held form factor, the Trimble Geo-Explorer 7 is an example of one of these. They now also have the ability to utilise NRTK, bringing there accuracies to within 0.5m (or better). The issue with phones and tablets is that, unlike dedicated systems, you have less control over how the coordinates are recorded. They don't take into account things like multipath (GPS signal bouncing off buildings, Ground etc.) The number of satellites (the more the better) Most survey kits wont record a point with less than 5 satellites. There is a way to get an idea of the accuracy for your proposed device. Take several readings over a day (7 or more) of 2 fixed points approx 50m apart, every day, for a week. Then compare the results. you will have a spread of points, none of which are likely to be perfect, but will give you an idea of the accuracies of the device, the spread of the points being your expected error. A shorter test over a day would yield similar results but over a week, you would have a more comprehensive result. I have seen some tests, where accuracies with an i-Phone were stated as +-3m. One other thing you should all note when using a phone or similar device to record your location, Use the native Latitude and Longitude to record the position, don't use the device to transform the coordinates to some other CRS. Use a dedicated CRS Transformation tool on a desktop/Laptop computer to convert to your desired CRS. Handhelds are not suitable for that purpose. I hope this helps!! Regards, Richard. On 03/04/2014 12:30, Leo Kris Palao wrote: Hi QGIS Users, I would like to inquire if there are some user that already assessed the positioning (location) accuracy of tablet vs commercial gps. We would like to use qgis android for fieldwork. We would also like to try qmap. Thanks, Leo ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user ** Email Disclaimer: http://www.opw.ie/en/disclaimer/ ** attachment: richard_mcdonnell.vcf___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Tablet vs GPS accuracy
On 2014/04/03 17:09, Richard McDonnell wrote: The issue with phones and tablets is that, unlike dedicated systems, you have less control over how the coordinates are recorded. They don't take into account things like multipath (GPS signal bouncing off buildings, Ground etc.) The number of satellites (the more the better) Most survey kits wont record a point with less than 5 satellites. and There is a way to get an idea of the accuracy for your proposed device. Take several readings over a day (7 or more) of 2 fixed points approx 50m apart, every day, for a week. Then compare the results. you will have a spread of points, none of which are likely to be perfect, but will give you an idea of the accuracies of the device, the spread of the points being your expected error. A shorter test over a day would yield similar results but over a week, you would have a more comprehensive result. I have seen some tests, where accuracies with an i-Phone were stated as +-3m. Surely this test is not relevant in any way, as when he is in the field (which could be a city centre), the accuracies would vary from his test site. The importance of such test is however that it makes the user _fully_ aware that the coords on the screen are not necessarily the position the GPS receiver IS actually at (at that time). People often seem to forget that a GPS screen is exactly like a TV screen - what you see on it is not necessarily the truth :-) -- === Zoltan Szecsei PrGISc [PGP0031] Geograph (Pty) Ltd. GIS and Photogrammetric Services P.O. Box 7, Muizenberg 7950, South Africa. Mobile: +27-83-6004028 Fax:+27-86-6115323 www.geograph.co.za === ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Tablet vs GPS accuracy
I agree with the points Richard has made here. I mentioned in an earlier message on this topic that I'd done a lot of testing with smartphones vs consumer gps see http://www.open.ac.uk/blogs/otih/?p=466 for details on some of the tests. Also tested consumer grade gps and a range of other surveying techniques with results and discussion shown here: http://oro.open.ac.uk/30066/ From: Richard McDonnell [richard.mcdonn...@opw.ie] Sent: Thursday, April 03, 2014 4:09 PM To: Leo Kris Palao Cc: QGIS Mailing List Subject: Re: [Qgis-user] Tablet vs GPS accuracy Hi, It all boils down to the level of accuracy your job requires, Commercial or Survey Grade GNSS (Global Navigation Satellite System) now utilises NRTK (Network Real Time Kinematic) which can produce sub centimetre accuracies. We have found that the accuracies is often too good, with our surveys conflicting with Maps. We have seen +-40mm accuracies in the field, where a stake in the ground is surveyed and the kit can take us right back to the point days later, to within 40mm. it is worth noting that Survey grade GPS has a stated accuracy of sub meter without NRTK. The next step down in accuracies would be GPS enabled Field Computers, again a dedicated kit but hand held form factor, the Trimble Geo-Explorer 7 is an example of one of these. They now also have the ability to utilise NRTK, bringing there accuracies to within 0.5m (or better). The issue with phones and tablets is that, unlike dedicated systems, you have less control over how the coordinates are recorded. They don't take into account things like multipath (GPS signal bouncing off buildings, Ground etc.) The number of satellites (the more the better) Most survey kits wont record a point with less than 5 satellites. There is a way to get an idea of the accuracy for your proposed device. Take several readings over a day (7 or more) of 2 fixed points approx 50m apart, every day, for a week. Then compare the results. you will have a spread of points, none of which are likely to be perfect, but will give you an idea of the accuracies of the device, the spread of the points being your expected error. A shorter test over a day would yield similar results but over a week, you would have a more comprehensive result. I have seen some tests, where accuracies with an i-Phone were stated as +-3m. One other thing you should all note when using a phone or similar device to record your location, Use the native Latitude and Longitude to record the position, don't use the device to transform the coordinates to some other CRS. Use a dedicated CRS Transformation tool on a desktop/Laptop computer to convert to your desired CRS. Handhelds are not suitable for that purpose. I hope this helps!! Regards, Richard. On 03/04/2014 12:30, Leo Kris Palao wrote: Hi QGIS Users, I would like to inquire if there are some user that already assessed the positioning (location) accuracy of tablet vs commercial gps. We would like to use qgis android for fieldwork. We would also like to try qmap. Thanks, Leo ___ Qgis-user mailing list Qgis-user@lists.osgeo.orgmailto:Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user ** Email Disclaimer: http://www.opw.ie/en/disclaimer/ ** -- The Open University is incorporated by Royal Charter (RC 000391), an exempt charity in England Wales and a charity registered in Scotland (SC 038302). ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Tablet vs GPS accuracy
I was just looking in to this issue. Dr. Paul Zandbergen at the University of New Mexico has two publications relating to smart phone assisted GPS accuracies and including findings on the hybrid locational systems they utilize. Good stuff! http://www.paulzandbergen.com/files/Zandbergen_Barbeau_JON_2011.pdf http://onlinelibrary.wiley.com/doi/10./j.1467-9671.2009.01152.x/abstract Kurt ** Kurt Menke, GISP Bird's Eye View www.BirdsEyeViewGIS.com http://www.birdseyeviewgis.com/ Work: 505-265-0243 Cell: 505-362-1776 ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Tablet vs GPS accuracy
Hi Guys, Thanks all for your valuable insights about my inquiry. I really appreciate your comments. I can use your comments as reference on how we will also evaluate GIS applications in Tablets. Our application mainly falls on agriculture. We want to use the tablets for surveying in Rural areas. And we want to use QGIS android so we can load our shapefile and raster maps for validation. On the other hand, we will also want to use tablets to take location of field corners of farmers field to get the plot size (this is where accuracy is important). I observe that when there is a wifi the location significantly increases in tablets. But of course, wifi is not available in rural areas. So, if we will use tablet we will just rely on available GPS signal, weather, and the device. Thank so much, and again I really appreciate the comments, -Leo On Fri, Apr 4, 2014 at 2:20 AM, Michael.Dodd michael.d...@open.ac.ukwrote: I agree with the points Richard has made here. I mentioned in an earlier message on this topic that I'd done a lot of testing with smartphones vs consumer gps see http://www.open.ac.uk/blogs/otih/?p=466 for details on some of the tests. Also tested consumer grade gps and a range of other surveying techniques with results and discussion shown here: http://oro.open.ac.uk/30066/ From: Richard McDonnell [richard.mcdonn...@opw.ie] Sent: Thursday, April 03, 2014 4:09 PM To: Leo Kris Palao Cc: QGIS Mailing List Subject: Re: [Qgis-user] Tablet vs GPS accuracy Hi, It all boils down to the level of accuracy your job requires, Commercial or Survey Grade GNSS (Global Navigation Satellite System) now utilises NRTK (Network Real Time Kinematic) which can produce sub centimetre accuracies. We have found that the accuracies is often too good, with our surveys conflicting with Maps. We have seen +-40mm accuracies in the field, where a stake in the ground is surveyed and the kit can take us right back to the point days later, to within 40mm. it is worth noting that Survey grade GPS has a stated accuracy of sub meter without NRTK. The next step down in accuracies would be GPS enabled Field Computers, again a dedicated kit but hand held form factor, the Trimble Geo-Explorer 7 is an example of one of these. They now also have the ability to utilise NRTK, bringing there accuracies to within 0.5m (or better). The issue with phones and tablets is that, unlike dedicated systems, you have less control over how the coordinates are recorded. They don't take into account things like multipath (GPS signal bouncing off buildings, Ground etc.) The number of satellites (the more the better) Most survey kits wont record a point with less than 5 satellites. There is a way to get an idea of the accuracy for your proposed device. Take several readings over a day (7 or more) of 2 fixed points approx 50m apart, every day, for a week. Then compare the results. you will have a spread of points, none of which are likely to be perfect, but will give you an idea of the accuracies of the device, the spread of the points being your expected error. A shorter test over a day would yield similar results but over a week, you would have a more comprehensive result. I have seen some tests, where accuracies with an i-Phone were stated as +-3m. One other thing you should all note when using a phone or similar device to record your location, Use the native Latitude and Longitude to record the position, don't use the device to transform the coordinates to some other CRS. Use a dedicated CRS Transformation tool on a desktop/Laptop computer to convert to your desired CRS. Handhelds are not suitable for that purpose. I hope this helps!! Regards, Richard. On 03/04/2014 12:30, Leo Kris Palao wrote: Hi QGIS Users, I would like to inquire if there are some user that already assessed the positioning (location) accuracy of tablet vs commercial gps. We would like to use qgis android for fieldwork. We would also like to try qmap. Thanks, Leo ___ Qgis-user mailing list Qgis-user@lists.osgeo.orgmailto:Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user ** Email Disclaimer: http://www.opw.ie/en/disclaimer/ ** -- The Open University is incorporated by Royal Charter (RC 000391), an exempt charity in England Wales and a charity registered in Scotland (SC 038302). ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
