China GPS Offset Values

[gdkcan]

Is there a table that lists the current locations you have Offset values for? Is there anything end users can do in China to supply updates to your offset values? I am staying in Nanjing now and find that the offset values do not appear to be present in the application.

Regards,

Gerry

[divzero]

Hey Jerry,

in GPS Log -> Settings -> Advanced Settings -> under "Map Offsets", tap "Update Map Offset Data".

I have added another data point in Nanjing for you

If you still find you have big offsets, please give me the lat/long of the problem area and I can add a new point specially for that area.

If you plan to visit another place, please tell me ahead of time and I can get a point for you. I plan to open this up and let anyone contribute data points... but I have no time, so for now we can do it like this

Please let me know if this works.

Enjoy using GPS Log in China!
Will

[gdkcan]

Thanks,

This has fixed my issue in Nanjing! I plan on logging the subway exits now

It's shameful that Google doesn't seem to be able to fix or care enough about end users enough to explain why they don't fix this issue themselves.

Gerry

[divzero]

You're welcome.

hehe subway exits... always a good thing to log I find

Apparently it's a licensing thing. Google would have to pay more to license the non-offset maps for China, so they don't. No idea how this affects users with chinese-sold iPhones... can't imaging people paying so much RMB for something with inaccurate maps.

At least Google has better China support than Bing Maps... if you are using Bing Maps with an english-language local, all you get are the main roads... ._.

And, at least GPS Log can compensate for this deficiency!

BTW. the satellite imagery is always accurate, if you find yourself in an area not covered by GPS Log then switch to that (not great for street names, but OK if you're looking for a lake or something.

Cheers,
Will

[Dan Lyke]

I've been away from GPS Log for a while, so I may be stepping in with solutions to problems that aren't really there, but are "Map Offsets" really a problem of Datums? And, if so, would simply integrating Proj4 be the right solution? That way those of us who have been known to do our own Datum reprojections don't get confused by whatever's going on under the hood.

[divzero]

Hey Dan,

Welcome back! Good to see you again.

Actually the problem is more insidious. In China, Google's street maps, while incredibly detailed, are intentionally offset by several blocks. Apparently it's due to some fee Google isn't paying, I don't know for sure. But the net result is that the street maps don't line up with the satellite imagery!

This feature attempts to correct for some of these offsets. It only affects countries where I collect this offset data, and currently that is just China (though there may be others). It's not a perfect solution, but it's better than nothing.

Each offset value has a range of effect, less than 200km. So you won't get any errors in America or any other country (and you can just turn the whole feature OFF as well).

If you see me talking about datums in relation to this feature, I'm referring to datum in the generic sense, i.e. "single piece of data", not a geodetic datum. Maybe I should pick a different term given the ambiguity

Proj4 looks pretty interesting.

How have you been? Working on any cool gps related projects? Any updates to MapATrek.com recently?

Cheers,
Will

[Dan Lyke]

No new stuff with GPS Log, been ankle deep (and standing on my head) in some other projects, though I do want to make sure I get some of the new uploading stuff working better.

Proj4 is cool, but only if you really have to deal with multiple datums, and that implies maps which aren't WGS84/NAD83, and I'm guessing Google Maps is attempting to rework everything into that. But, of course, I take a U.S. centric view of things, where we only really have two datums for large scale maps, and NAD27 is gradually disappearing.

But I'm also well aware that US centric views often miss large potential markets...