Same place - different Lat & Long between Google and Gar

[BigJohnD]

I'm going to France in a week or so and am creating various waypoints/favourites for the Garmin.

Some of the places have been a bit tricky to find but what has shown up is that Google Map's Lat & Long differ considerably from Garmin's - by maybe 150m. Not much on a country road, but the wrong street in a town.

While I didn't really expect an exact match, I didn't expect such a great difference.

Example:
Address: 6 Place de l'Église, 51700 Troissy. France
Google Maps:          N49.08107°, E3.71022°
Garmin Basecamp:  N49.08038°, E3.71195°

This pic shows the address (bed icon) as per Garmin Basecamp but the Google calculated location is some 150m away to the NW. Crazy.



Do they use different satellites?

[Privateer]

Hi BigJohnD,

I create POIs for both TomTom and Garmin, mainly for the UK but I have done a lot of Disney ones for France, USA, Hong Kong, Japan, and China. The only one that should cause a problem is China due to using a different map datum.

Before I go any further can I confirm that you're mentioning that the address e.g. "6 Place de l'Église, 51700 Troissy. France" is calculated to be in a different location by the Garmin unit, Garmin Basecamp, and Google?

Whilst I have a Garmin I don't use basecamp.

Regards,
_________________
Robert.
iPhone 6s Plus, iOS 14.0.1: iOS CamerAlert v2.0.7
TomTom GO Mobile iOS 2.3.1; TomTom (UK & ROI and Europe) iOS apps v1.29
Garmin Camper 770 LMT-D

[sussamb]

Do you know which is more correct? It could just be due to different rounding algorithms.
_________________
Where there's a will ... there's a way.

[Privateer]

[M8TJT]

But what are you using as the search? The POI name? Address or lat/lon.
I.e. If the POI name, then Google and Garmin might have a different lat/lon for it compared with Garmin.

Or are you saying that N49.08107, E3.71022 takes you to a different place on the two different maps?

[dales]

It looks like your Datum is wrong in Basecamp.

Try Edit..Options...Measurement..Datum at the bottom.

You may have it set for OSGB.
Anyway, setting it to WGS 84 should fix it.

Dales
_________________
nuvi 2599LMT-D, oregon 700, basecamp, memory-map.

[Privateer]

I'm using the address "6 Place de l'Église, 51700 Troissy. France" to search in Google Earth.

I then switched to Street View and 'strolled' around the vicinity to find a property with No 6 on it. Although to be fair, Google Earth does take you very close.

I then zoomed in, placed the mouse pointer to the green double gates of No 6 and grabbed the coordinates, which are 49.081011,3.710116.

If you put "49.081011,3.710116" into a POI your SatNav will take you there and tell you which side of the road to find the destination - if of course it normally tells you that.

Regards,
_________________
Robert.
iPhone 6s Plus, iOS 14.0.1: iOS CamerAlert v2.0.7
TomTom GO Mobile iOS 2.3.1; TomTom (UK & ROI and Europe) iOS apps v1.29
Garmin Camper 770 LMT-D

[Kremmen]

[sussamb]

Setting the correct datum is vital
_________________
Where there's a will ... there's a way.

[BigJohnD]

[jad12]

Good good BigJohnD, you have it sorted. However you may find similar in other countries also. Datums have been mentioned.

Goople Maps, and Earth, are global and appropriately use a global system, the best fit WGS84 spheroid, what GPS lat/long is based on. Local maps, probably based on pre GPS local reference systems (eg OSGB) have lat/long on their own best fit spheroid (OSGB is Airey). France will have its own national mapping system. 150m difference can be expected. OSGB WGS84 difference is 100m around London. It differs over the UK but they never get close enough.

I don't think satnav specs ever state datums, like to know if they do, but if using a French map in your Garmin I would expect it to adjust GPS input to local. The sum to do it will be programmed in. Can you use a UK based satnav map in France? If you can it should work out ok. If compared to a French based map though there will again be differences. I believe France is also on a different projection Lamberts Conic rather than our Transverse Mercator.

This geodetic stuff can get a bit involved but as long as you are aware that there may be differences and different maps can be on different systems it shouldn't be too big a problem.

Cheers
_________________
A school of dolphins A flock of birds A pride of lions A lost of navigators

[sussamb]

@jad12 Your GPS is exactly that, Global, and will work wherever you are.
_________________
Where there's a will ... there's a way.

[M8TJT]

Then why do the maps in China differ from the sat view by some margin?
It wouldn't be because the maps are drawn to one reference datum and the sat view to a different one would it? How global is that:roll:

[dales]

That's a decision by the Chinese government.
Chinese satnav maps contain an offset. If you have a satnav bought in China, that will correct the offset. But any other satnav will show the offset view.

Dales.
_________________
nuvi 2599LMT-D, oregon 700, basecamp, memory-map.

[sussamb]

Yes, China is funny like that
_________________
Where there's a will ... there's a way.

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