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Hi FME folks,

I'm trying to reproject these coordinates:
 SRID=3857;POINT(530385.593659309 6910697.223221438) into a EPSG:28992 point.

I notice the result FME gives me differs a lot from other tools / methods - the difference is about 12 cm.

My method:

1: Scraping JSON: "geometrie": "SRID=3857;POINT(530385.593659309 6910697.223221438)"
2: CoordinateSystemSetter: EPSG:3857
2: Use regex to extract Lat / Lon.
3: Create point using VertexCreator
4: Reprojector: Source: EPSG:3857 | Destination: EPSG:28992

Results FME:

  • POINT (112820.96207905837 513493.7654737713)

 

Other tools used:

  • Internal geocoding tool: POINT (112820.87254041698 513493.83730794006)
  • ChatGPT conversion: POINT (112820.87254041698 513493.83730794006)
  • Google Gemini conversion: POINT (112820.87254042 513493.83730794)
  • Grok conversion: POINT (112820.87254042 513493.83730794)
  • Python conversion: POINT(112820.873 513493.837)
  • SQL conversion: POINT (112820.87254041698 513493.83730794006)

 

So now I wonder, why is FME saying A and all the other tools I've used; B.
What's causing this ~12 cm difference?
Perhaps I've messed up the reprojection proces in FME? If so, how to do it properly?


(I'm using FME(R) 2022.2.3.0 (20230131 - Build 22789 - WIN64))

EPSG:3857 is WebMercator and that uses WGS84. EPSG:28992 is based on ETRS89. That means to be exact you would need actually two conversions, although FME doesn't seem to be make a difference between ETRS89 and WGS84.

It is possible nowadays to convert to RD with just EPSG codes, but not with the Reprojector because you can't define the EPSG it should use for the transformation.

Therefor I recommend to use the Custom Transformer called RdNapTrans2018 which will take care of special adjustments from the pseudo-grid which could be around 10 centimeters. I think that will solve your problem.

 

Okay, I've looked into it some more. I'm not getting the exact same numbers as you when you look at sub milimeter precision. But at that level it is the same and to my surprise it is at that level the same between the Reprojector and RdNapTrans2018.

It might be then that the difference you see comes by a the missing transformation between WGS84 and ETRS89. If I use a Reprojector to transform your coordinate to ETRS89 I get 4.764534852609632, 52.607356651527915. If I give that as input into Online coördinatentransformatie - NSGI it is the same as what FME is giving. 

A solution would be to use the EsriProjector where you can also define which Transformation to use and even set the epoch if you know at what date your data is measured.

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