Impactful Coordinate Changes for Pleiades Transition

As part of the Pleiades Data Corporation transition and as it was communicated on the transition webinar, we are updating all Pleiades coordinates in Western Canada to NAD83(CSRS v6) Epoch 2010.00.  This will allow users to work from a common reference frame across Alberta and British Columbia assuring consistency, repeatability and stability for the long term.  We are also updating the names and RTCM IDs of every station as well to provide a clear and consistent break and remove any doubt or confusion on what network or reference system you are working in.

All Pleiades users need to understand the coordinate changes being made as part of this transition are MAJOR shifts and need to be accounted for at the rover level for existing projects or to assure ties to previous work.

Every coordinate adjustment made by RTN operators has the potential to impact customers and it is because of this that the SmartNet Team always makes these decisions with a great deal of care and consideration because of these impacts.  To better help you understand the impacts of these changes as part of the transition, please see the information below.

Why are we doing this coordinate update?

SmartNet North America has had an agreement in principle since we launched with NRCAN to assure a high quality, standard set of coordinates were available to our customers.  Late in 2014, we entered into a formal agreement with NRCAN as part of the NRCAN RTK Service Provider Compliance program.  

As part of this program, we are required to adopt the NAD83(CSRS v6) Epoch 2010.00 broadcast coordinates that are calculated and provided by NRCAN to assure our customer base is operating on the appropriate National Spatial Reference System in Canada.  Because Pleiades to this point has not been part of the NRCAN Compliance program, NRCAN derived coordiantes are not available, so as part of the transition we will be using SmartNet derived coordinates which should fit to the NSRS in the sub-centimeter range.

Once all data streams are transitioned, SmartNet will immediately advise NRCAN of the changes to allow them to begin their calculations so that we can make sure the SmartNet derived coordinates are in agreement with NRCAN.  We expect to receive NRCAN derived coordinates in January 2017 to analyze any differences and will advise the Western Canada user base should there be any variances.

As part of this RTK Service Provider Compliance program there is a variance threshold for the station coordinates we are allowed to operate in, so the SmartNet coordinates that are being put in place will most likely not need to be changed again once we receive the NRCAN derived coordinates.

What does this adjustment mean to me?

In very simple terms it means the broadcast position of every station that was part of the Pleiades network is going to change.  We have been asked what the estimated change will be on a number of occasions by the Pleiades user base.  As the Pleiades network had not adopted a common reference frame to bring all stations into alignment, the coordinate change from station to station, province to province are vary to a large degree.

We have attached a spreadsheet to this article listing both the broadcast (coordinates you use to calculate a position relative to the reference station) and processing/physical coordinates (coordinates we use to calculate the network correction).

Please refer to the "Site Information Search" tool to determine the amount of the shift (or click on the site code below), you can view the current and superseded coordinates, we encourage you to watch this short video to learn more about the tool - LINK.

What reference frame and epoch are we moving to?

We will still be in the NAD83(CSRSv6) reference frame to stay consistent with the NSRS and we are moving to a 2010.00 epoch.

How can I get back to my old coordinates?

You can also perform your own local transformation, localization or calibration.  For more information about using this technique, please click here - LINK.

Why are you not providing a transformation that would allow us to go between new and old coordinates?

In our eyes, this is not the right approach.  The coordinates changes are too large and too varied to produce an accurate and reliable transformation on a large scale.

We don't want to induce additional error by having an inaccurate transformation or complexity by having multiple different transformations to fit smaller areas.  Local site based transformation are a more robust and logical solution to address these large shifts on a site by site basis.

Are you providing a way to transform from NAD83(CSRSv6) Epoch 2010 to other realizations or epochs?

Unfortunately no, there is not an easy way to do this at scale.  See the note from Michael Craymer at NRCAN

'There is no easy or simply transformation for your users to get NAD83(CSRS)v3 epoch 1997 or NAD83(CSRS)v4 epoch 2002 from RTK-determined coordinates in NAD83(CSRS)v4 epoch 2010.  The only current solution is to use/interpolate the NAD83(CSRS)v6 velocity grid to propagate v6 coordinates from epoch 2010 to 1997 and 2010. That involves using an NTv2-type of interpolation of a fairly large velocity grid. We provide on-line and desktop software to do this (TRX):

 http://www.nrcan.gc.ca/earth-sciences/geomatics/geodetic-reference-systems/tools-applications/10925#trx

This software is obviously not a real-time solution. Also, note that the resulting NAD83(CSRS)v6 epoch 1997 & 2002 coordinates are not entirely compatible with v3 & v4. The remaining residual differences after propagating to the same epoch represent effects due to less data and older adjustment methodologies in v3 and v4. I have presented these differences in the last several CGRSC meetings, including a summary at the meeting last Spring (attached below). For horizontal coordinate differences, see slide 10 for “v6.0.0(1997.0) – v3.0.1(1997.0)” and slide 11 for “v6.0.0(2002.0) – v4.0.0(2002.0)”. For vertical differences, see slides 14 and 15, respectively. The horizontal differences in BC appear to be less than a cm except near/along the coast for v3 (max 1.5 cm) and less than a cm everywhere for v4 . Vertical differences are about a cm (larger in the north) for v3 (max 5 cm) and about half a cm (a cm in the north) for v4 (max 4 cm).'

As mentioned previously, SmartNet does not want to be responsible for attempting to determine a transformation and inducing additional errors at the user level while representing what we are providing is accurate or proper.  

Users may create their own transformations either by doing simple site calibrations / localizations / transformations or they can work to create a more complex 7 parameter Helmert transformation for a larger area, but again this could introduce unforeseen errors or consequences.

How do I see the current coordinates and superseded coordinates?

All current and superseded coordinates are available on the SmartNet User Portal.  You can find a station's information by using the "Site Information Search" tool, then you can see the current broadcast and processing coordinate, as well as find a button that will allow you to view all the superseded positions as well.

For more information on using the "Site Information Search" tool, we encourage you to watch this short video - LINK.

What do you mean by processing or physical coordinates?

Please see our related support article on processing and physical coordinates - LINK

How do I get support to better understand what this adjustment means?