send location now error in china

[boommanpro]

When using the owntracks iOS app in China, the location reported by 'send location now' differs from the latitude and longitude reported by MQTT.

[ckrey]

Sent location now is transmitted the same way as other location messages (MQTT or HTTP).
Send location now uses the current location as shown on the map.

As we are not based in China you will have to provide some examples

[boommanpro]

mqtt
send location now
{ "_type": "location", "acc": 9, "alt": 41, "batt": 20, "bs": 1, "cog": 7, "conn": "m", "inregions": [], "inrids": [], "lat": 39.980035, "lon": 116.470433, "m": 2, "motionactivities": [ "stationary" ], "p": 99.628, "t": "u", "tid": "2F", "tst": 1754399511, "vac": 3, "vel": 0 }

move auto send
{ "_type": "location", "acc": 6, "alt": 41, "batt": 20, "bs": 1, "cog": 7, "conn": "m", "inregions": [], "inrids": [], "lat": 39.978731, "lon": 116.464319, "m": 2, "motionactivities": [ "stationary" ], "p": 99.628, "t": "t", "tid": "2F", "tst": 1754399488, "vac": 3, "vel": 0 }

@ckrey

[ckrey]

Which location do you think is the "correct" one?

Please share your settings (ignoreInaccurateLocations, locatordDisplacement, ...) with us.
And please share the log file containing the relevant timestamp and a few minutes earlier with us (via mail to support@owntracks.org)

[ckrey]

Maybe explained here.

[boommanpro]

I know that the map in China is special, but I sent the information from the same location, and there is a big difference in geographical position through two methods. Is there a difference in the implementation logic here? Where is this issue, and can I also help to fix it?

[ckrey]

Both locations are taken from iOS' Core Location framework, though the send location now uses the current user position from the Map Kit because it is updated more frequently while on screen.
I don't know what the issue is, there are no hints in the documentation. But I guess the Map does the corrections necessary for the Chinese Coordinate system.
No idea how to fix this or how to find out if my guess is valid.

[SirTypesALot]

I did some experimentation with this issue last year, the way it behaves is indeed sort of weird.

First of all, a quick context class. China's GIS providers uses a different coordinate system called GCJ-02 instead of the international standard WGS84. GCJ-02, also known as the Mars coordinate system, because it is a non linear coordinate system, meaning the distortion range and direction is different for each WGS84 coordinates that you try to plot on a Chinese map.

As for OwnTracks, the coordinates sent in a location update in the background uses the WGS84 system, while coordinates of location update sent manually uses GCJ-02. I don't know why the OS uses two coordinates system while in China.

With that being said, there are algorithms that can perform rough estimation and conversions between the two systems.