Mapping in China (WGS 84 <-> GCJ-02)

[CharlieS]

Hi all.

Does anyone have experience using Alteryx for mapping solutions in China? The WGS84 coordinate system doesn't line up with the GCJ-02 projection system used by some sources in China. Alteryx spatial tools support custom projection systems via WKT, so ideally that code exists somewhere. 

The options I've found so far involve Baidu API calls which isn't ideal for complex polygons or at scale. I'd love to hear any insight or alternative options for this scenario.

Edit: Calling in some backup. @EricM @Philip 

[EricM]

Hi @CharlieS, 

I have zero experience working with Chinese geospatial data, but this was an interesting learning experience -  thank you for posting!  

Defining custom projections based on WGS84, NAD83 datums etc. is no problem in Alteryx as you know, but it looks like gcj-02 is China's own datum and it doesn't seem to be very accessible. 

I found some interesting stuff on the web, sharing here in case anyone else runs into this in the future: 

https://gis.stackexchange.com/questions/234202/are-there-epsg-codes-for-solving-china-gps-shift-prob...

https://en.wikipedia.org/wiki/Restrictions_on_geographic_data_in_China

Any of our other spatial gurus @StephenR @NickPa have any ideas?

Best, 

Eric

[CharlieS]

Thanks for joining in, @EricM; I wouldn't want you to miss out on any spatial fun. That Wiki page is what opened my eyes to the issue once the geocoding discrepancies came to light. 

Right now I'm looking into the Python from this GitHub to see if it's a viable option:

https://github.com/googollee/eviltransform

[NickPa]

GCJ-02 is a geodesic datum that is controlled by the Chinese government and not accurate for plotting GPS or spatial objections on top of it.  From a user perspective there seems to be minor value for Alteryx to develop or license the algorithm for translating WGS84 into GCJ02 and supporting Chinese mapping projects, in addition to the risk that comes from supporting this datum.

Alteryx has no plans at this time to support GCJ-02 geodesic datum.  We will review this requirement in the future as we see more demand in Chinese geo projects.

[CharlieS]

For future reference, we found the most useful information here:

https://wangbaiyuan.cn/en/baidu-map-api-position-offset-calibration-algorithm-2.html

Thanks @EricM and @NickPa for your help. I'm glad this post now exists for others to find.