Re: [Talk-ca] NAD83-SCRS vs WGS84 Reference systems
Hi all let me review what we received so far Richard wrote: "If I remember correctly, the current Can-US border came from IBC data. How does the current border line match the monument data that you are considering? Should they be identical and are they?" I have been told that IBC recomputed their coordinates 1-2 years ago (new compensation). I don't know if the border was obtained after they published the new coordinates. I've compared current border line with monument coordinates from IBC in southern Quebec. Even if for few coordinates the difference was up to 10 meter, the differences I found were usually within a meter. That is why I was considering keeping the CSRS coordinate as is. Brendan wrote: "I was musing on a similar topic just recently, which ... [reference]" I've read the document and I understand that a simple sequence of multiplication/addition on coordinate values will do the job. Cool! However, if it is that simple, what are those grid shift they are talking about (Google: grid shift wgs84 nad83 csrs)? A way to get more accurate results? "I assume you mean NAD83(CSRS) coordinates, by the way?" You are right! I probably used SCRS(1) because, as French is my native language, I've consulted French documents before going on the list :-) So, should we convert the IBC nad83-csrs coordinates to wgs84? yes: Real wgs84 coordinates - confusing info about nad83-csrs conversion no: Inaccuracy of 0-2 meters in wgs84, direct coordinate values on web site. Still don't know what the decision should be. Next time I'll have a simpler question !-) Cheers, Daniel (1) In French, SCRS stands for Système Canadien de Référence Spatiale -Original Message- From: Brendan Morley [mailto:morb@beagle.com.au] Sent: March-27-11 06:27 To: talk-ca@openstreetmap.org Subject: Re: [Talk-ca] NAD83-SCRS vs WGS84 Reference systems Daniel, I was musing on a similar topic just recently, which I've cc'd to: http://www.commonmap.org/blog/commonmaps-common-datum/2011-03-27 I assume you mean NAD83(CSRS) coordinates, by the way? My understanding is the de facto datum of OSM is WGS84/ITRF with epoch varying with the age of each entered coordinate, and planimetric accuracy at best 10 metres (at 10m, WGS84=ITRF). Given NAD83 and WGS84 are also within the 10m error, you could just argue that you can just upload the coordinates to OSM as is. Leave a note in the changeset (maybe per boundary way?) noting where the rigorous values can transformation methods can be found. However if you want to adjust the coordinates, you could try the NAD83->ITRF (WGS84) 7(+3 dynamic) parameter similarity (Helmert) conversion for areas without a better option. This paper is the best I've found on the matter; see Section 4 of: http://www.geod.nrcan.gc.ca/publications/papers/pdf/nad83csrs.pdf Remember that the coordinates start drifting with 2-3cm/annum velocity as soon as you enter then into OSM! Do you want to be this rigorous? Brendan On 27/03/2011 5:55 AM, Daniel Begin wrote: > Hi all, > > I need someone to confirm the following about reference system... > > Context: Paul and I are uploading US-Canada boundary monuments/turning > points to get a stable and verifiable information. The data is available > from their web site and I got the confirmation that the data can be used > without any restriction. The data can be found here... > http://www.internationalboundarycommission.org/products.html > > and it is available for NAD27 and NAD83-SCRS reference system. > > Context: For what I understand, The difference between NAD83-SCRS and WGS84 > is 0-2 meters. To get a rigorous transformation from NAD83-SCRS to WGS84 we > need to use shift grids describing the shift between NAD83 and NAD83-SCRS. > These grids should be available through provincial agencies but I have been > told that not all provinces have them available. > > Question1: Do I understand it properly? > > Question2: Considering that provided coordinates value/reference numbers can > be read directly from their web site, it make sense for me to use NAD83-SCRS > directly even if there is a 0-2 meter offset. Does it make sense for > everyone? > > Cheers, > > Daniel > > > > ___ > Talk-ca mailing list > Talk-ca@openstreetmap.org > http://lists.openstreetmap.org/listinfo/talk-ca > > ___ Talk-ca mailing list Talk-ca@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-ca ___ Talk-ca mailing list Talk-ca@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-ca
Re: [Talk-ca] NAD83-SCRS vs WGS84 Reference systems
Daniel, I was musing on a similar topic just recently, which I've cc'd to: http://www.commonmap.org/blog/commonmaps-common-datum/2011-03-27 I assume you mean NAD83(CSRS) coordinates, by the way? My understanding is the de facto datum of OSM is WGS84/ITRF with epoch varying with the age of each entered coordinate, and planimetric accuracy at best 10 metres (at 10m, WGS84=ITRF). Given NAD83 and WGS84 are also within the 10m error, you could just argue that you can just upload the coordinates to OSM as is. Leave a note in the changeset (maybe per boundary way?) noting where the rigorous values can transformation methods can be found. However if you want to adjust the coordinates, you could try the NAD83->ITRF (WGS84) 7(+3 dynamic) parameter similarity (Helmert) conversion for areas without a better option. This paper is the best I've found on the matter; see Section 4 of: http://www.geod.nrcan.gc.ca/publications/papers/pdf/nad83csrs.pdf Remember that the coordinates start drifting with 2-3cm/annum velocity as soon as you enter then into OSM! Do you want to be this rigorous? Brendan On 27/03/2011 5:55 AM, Daniel Begin wrote: Hi all, I need someone to confirm the following about reference system... Context: Paul and I are uploading US-Canada boundary monuments/turning points to get a stable and verifiable information. The data is available from their web site and I got the confirmation that the data can be used without any restriction. The data can be found here... http://www.internationalboundarycommission.org/products.html and it is available for NAD27 and NAD83-SCRS reference system. Context: For what I understand, The difference between NAD83-SCRS and WGS84 is 0-2 meters. To get a rigorous transformation from NAD83-SCRS to WGS84 we need to use shift grids describing the shift between NAD83 and NAD83-SCRS. These grids should be available through provincial agencies but I have been told that not all provinces have them available. Question1: Do I understand it properly? Question2: Considering that provided coordinates value/reference numbers can be read directly from their web site, it make sense for me to use NAD83-SCRS directly even if there is a 0-2 meter offset. Does it make sense for everyone? Cheers, Daniel ___ Talk-ca mailing list Talk-ca@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-ca ___ Talk-ca mailing list Talk-ca@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-ca
Re: [Talk-ca] NAD83-SCRS vs WGS84 Reference systems
On Sat, Mar 26, 2011 at 3:55 PM, Daniel Begin wrote: > Hi all, > > I need someone to confirm the following about reference system... > > Context: Paul and I are uploading US-Canada boundary monuments/turning > points to get a stable and verifiable information. The data is available > from their web site and I got the confirmation that the data can be used > without any restriction. The data can be found here... > http://www.internationalboundarycommission.org/products.html > > and it is available for NAD27 and NAD83-SCRS reference system. > > Context: For what I understand, The difference between NAD83-SCRS and WGS84 > is 0-2 meters. To get a rigorous transformation from NAD83-SCRS to WGS84 we > need to use shift grids describing the shift between NAD83 and NAD83-SCRS. > These grids should be available through provincial agencies but I have been > told that not all provinces have them available. > > Question1: Do I understand it properly? > > Question2: Considering that provided coordinates value/reference numbers can > be read directly from their web site, it make sense for me to use NAD83-SCRS > directly even if there is a 0-2 meter offset. Does it make sense for > everyone? Bonjour Daniel! We do have others on this list with experience in re-projection. I hope they'll join in. I've asked about the shift grids on #osm-dev. If I remember correctly, the current Can-US border came from IBC data. How does the current border line match the monument data that you are considering? Should they be identical and are they? Could we pop this data into a tile overlay layer so we can look at it on existing OSM data (without the import)? Best regards, Richard ___ Talk-ca mailing list Talk-ca@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-ca
[Talk-ca] NAD83-SCRS vs WGS84 Reference systems
Hi all, I need someone to confirm the following about reference system... Context: Paul and I are uploading US-Canada boundary monuments/turning points to get a stable and verifiable information. The data is available from their web site and I got the confirmation that the data can be used without any restriction. The data can be found here... http://www.internationalboundarycommission.org/products.html and it is available for NAD27 and NAD83-SCRS reference system. Context: For what I understand, The difference between NAD83-SCRS and WGS84 is 0-2 meters. To get a rigorous transformation from NAD83-SCRS to WGS84 we need to use shift grids describing the shift between NAD83 and NAD83-SCRS. These grids should be available through provincial agencies but I have been told that not all provinces have them available. Question1: Do I understand it properly? Question2: Considering that provided coordinates value/reference numbers can be read directly from their web site, it make sense for me to use NAD83-SCRS directly even if there is a 0-2 meter offset. Does it make sense for everyone? Cheers, Daniel ___ Talk-ca mailing list Talk-ca@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-ca
