OT How does GMaps know elevation?

[rbowman]

[Rob]

The latter. In regions with new streets or buildings you can see streets on the streetview and bare land in the sat view.

[Rob]

Streets are shown in new developments even when they not yet have been laid, but have been submitted as planned.

[Rod Speed]

Problem with that line is that the altitude from GPS is much less accurate than doing it the other ways, particularly using lasers from satellites and only works where the car actually goes.

Once you have the data from the satellites, there isnt any point in adding the less accurate data from the cars.

[Rod Speed]

They go pretty fast when the Faroe Islanders are trying to f*ck them.

[Rod Speed]

Here they get it from the operation that is doing the new streets.

That wouldn't give them the street names.

Not send google so much as update their database and google accesses those. We have seen it take a while before the google map is updated with new ones. This is one example.

and Gillmartin are now well past Haines with new houses being built on the new bits of Tucker and Gillmartin now.

With ours they are on the council maps, what you call municipalitys.

Ours work fine for bicycles but google doesn't use them for bikes.

[Rod Speed]

Can you post a proper link ? I can only get google maps to show photos of it.

[Paul Hovnanian P.E.]

Several. USGS probably releases topographical data. There is also data from the Shuttle Radar Topography Mission (SRTM). See:

Several projects attached to the Open Street Map project inculde tools to integrate SRTM data into maps installable on various GPS devices.

[Rob]

I guess it depends on the quality of your local database. Here we see new streets and quarters on Google Maps that do not yet exist in reality (but have been planned and will be built).

[Rod Speed]

The local database is fine, it just takes google a long time to use the updates.

That not necessarily due to the quality of the local database.

We saw the google car show up again here almost 18 months ago, after it had been here previously more than 10 years previously. The second time they only zoomed thru some of the main streets in town and didn’t even bother to visit the new roads and houses.

[rbowman]

I do a lot of work with local GIS departments and the quality is extremely variable. Some are on top of it and others are completely out of their depth. At least one uploads their edits to ESRI and not Google. Google puts their dispatch center in the wrong place so they don't exactly trust them.

There are several big players like HERE (formerly NavTeq) and TeleAtlas. Licensing their data isn't cheap and depends on how frequently you want it updated. TIGER/Line is the US Census Department and the data is free but the update cycle is slow. It's interesting to take the data for the same area from several different sources, overlay it, and see where it differs.

[Rob]

It likely is all coincidence. They fetch the info once every so many years, and it could include very recent information or it could take several years.

This is not at all related to it. The google car does not map the streets, it collects data and pictures.

[Rod Speed]

Why would they do it so slowly ?

And the google maps don’t show the new ones in bursts like that.

Duh.

[dpb]

I dunno who's the responsible party, but for years after the County revised the 911 naming system GPS maps from all sorts of places such as the builtin with various newer cars, the wife's Garmin (even w/ updates) and Google maps all were wrong terribly in many different ways. Never could understand how could be so many different ways they could all be wrong, particularly when the County naming system never looked like any of the versions displayed.

UPS was all over the County trying to figure out how to deliver stuff -- which was another illustration of the computer taking over for thinking--the county roads are all on section lines on straight NS/EW grid lettered beginning with 'A' on the west to 'Y' on the east and '1' to '27' from south to north. Road numbers are based on the mileage from the starting county line in miles and fractions thereof expressed as mmfff. So, it takes very little in the way of a map to find any where in the county if one can just count...it's particularly easy for NS, w/ EW you do have to adjust for letter position in the alphabet.

I explained the system to several drivers more than once who were on the east side of town looking for an address in the 4000 or 5000 numbers; I think only one ever actually figured it out.

It took some 7-10 years before most were right -- Google maps I think is now ok, finally -- yeah, at least in the main. They've got our road named for the continuation of the street name in town when it leaves the city instead of the county number but at least the ones that are numbered are done so correctly now.

[Mike S]

How so? Wikipedia says this:

"Global Positioning System (GPS) receivers can also determine altitude by trilateration with four or more satellites. In aircraft, altitude determined using autonomous GPS is not reliable enough to supersede the pressure altimeter without using some method of augmentation"

[rbowman]

Barometric altimeters aren't that great either. I haven't flown in years so the procedure might have changed but airports would have their elevation prominently marked. Part of the preflight was setting the altimeter to match.

[Swer]

That’s because air pressure changes. Laser height measuring from satellites and planes for mapping works fine and is a lot more accurate than GPS.

[Scott Lurndal]

[etpm]

Why is laser measuring much more accurate than GPS? They both use light and clocks. Eric

[etpm]

move the same speed as lasers. What is it about using lasers that makes them more accurate? Eric