[PROJ] Sweref99 Cartesian

[Jivall Lotti]

Yes, you can transform the position from the GNSS-receiver directly to XYZ with cct +proj=cart +ellps=GRS80 . It does not make any sense to transform from WGS84 to SWEREF 99 first. The difference between SWEREF 99 and WGS84 is today about 8 dm, and your position from the GNSS-receiver has probably a larger uncertainty,  so it does not matter if you use WGS84 or SWEREF 99 for the virtual location. But in the GNSS-processing with the virtual RINEX-file the coordinates are considered as accurate SWEREF 99-coordinates.
Best Regards, Lotti

Från: Roger Oberholtzer <roger.oberholtzer at gmail.com>
Skickat: den 21 april 2022 11:27
Till: Jivall Lotti <Lotti.Jivall at lm.se>
Kopia: PROJ <PROJ at lists.osgeo.org>
Ämne: Re: [PROJ] Sweref99 Cartesian

On Thu, Apr 21, 2022 at 9:39 AM Jivall Lotti <Lotti.Jivall at lm.se<mailto:Lotti.Jivall at lm.se>> wrote:
Hi Roger,
SWEREF 99 is a 3D geodetic reference system (the Swedish realisation of ETRS89) and can be expressed as geocentric cartesian coordinates (X Y Z) , geodetic coordinates (latitude, longitude and height) or a number of map projections where SWEREF 99 TM is the national one (whole Sweden in one zone). You can read more at Lantmäteriets webb page<https://www.lantmateriet.se/en/maps-and-geographic-information/gps-geodesi-och-swepos/Referenssystem/Tredimensionella-system/SWEREF-99/>.

You are right that SWEPOS virtual RINEX generator is requesting SWEREF 99 XYZ (and I understand it might be easier for you to use PROJ instead of out online transformation on the webb). All SWEPOS services are producing data in SWEREF 99, as this is the national reference frame. It means that when you process your GNSS-observations with the VRS reference data then you will get the results in SWEREF 99. (Therefore you should not use the accurate NKG-transformation from  ITRF2014 (WGS84) to SWEREF 99 – if your final results should be presented in SWEREF 99!)

Your original position from the GNSS-receiver is in WGS84 (current epoch) but I guess just on a few meter level and actually you just need a very approximate position to get your virtual reference near your own measurements. The position you input to SWEPOS VRS generator will be interpreted as SWEREF 99.

Hope it is now more clear!

I think so. So you mean if I provide the receiver's WGS84 lat/lng to, say,  cct +proj=cart +ellps=GRS80 , then the resulting locations should be adequate for requesting a virtual station at that WGS84 location?

--
Roger Oberholtzer
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/proj/attachments/20220421/7683b5ee/attachment.html>