OT How does GMaps know elevation?

[micky]

When you use google maps to choose a route between two locations, and
choose walking or bicycling, it also shows starting and ending elevation
and a graph that shows changes, so you can see how many and how big the
hills are. Also useful, of course, just for finding elevation without
any walking.

But how does it know elevation. If a GPS gets signals from 3
satellites, it can calculate location, and if it gets signals from 4 of
them, it can calculate elevation. But the calculation is made in the
GPS device, such as a smartphone. Google doesn't have GPS devices at
any random location the user picks, and it has no way to read satellite
signals.

Is there some topographical map underlying the google maps, even though
there is no way to display that map wwithin google?

 

[Jeff Urban]

Satellite.

 

[N_Cook]

On 30/07/2019 19:43, micky wrote:

When you use google maps to choose a route between two locations, and
choose walking or bicycling, it also shows starting and ending elevation
and a graph that shows changes, so you can see how many and how big the
hills are. Also useful, of course, just for finding elevation without
any walking.

But how does it know elevation. If a GPS gets signals from 3
satellites, it can calculate location, and if it gets signals from 4 of
them, it can calculate elevation. But the calculation is made in the
GPS device, such as a smartphone. Google doesn't have GPS devices at
any random location the user picks, and it has no way to read satellite
signals.

Is there some topographical map underlying the google maps, even though
there is no way to display that map wwithin google?

Check out a convenient Google height and you'll find its a load of junk.
In the UK luckily there are still a lot of surviving Ordnance Survey
benchmarks around and you can optically survey to them and easily get to
mm accurace if no more than 1-200m away (wrt the old map data containing
benchmark heights).
It is possible of course that the underlying land has risen or fallen
from post glacial isostatic rebound or water/oil extraction etc.
But even with mobile phone link dGPS (aGPS) surveying the
resolution/repeatability is no better than 15mm. And can easily be a lot
worse and without a second method (eg benchmarks) you won't know.
Outside the UK I've no idea if there are other networks of benchmarks.
I would like to find an "ap" where , as the GPS orbits are known , that
it would be possible to find times in the near future where 4 satellites
would be near enough overhead and none at lower elevation.
I wonder what sort of height determination you could get with that for
height determination.









--
Monthly public talks on science topics, Hampshire , England
<http://diverse.4mg.com/scicaf.htm>

 

[Andy Burns]

micky wrote:

Google doesn't have GPS devices at
any random location the user picks

Every user carrying a GPS enabled android device is crowd-sourcing data
for google, if someone's been there, google will know the altitude.

 

On 7/30/19 2:43 PM, micky wrote:

Is there some topographical map underlying the google maps, even though
there is no way to display that map wwithin google?

If you click on the GMaps Menu icon (3 line "hamburger" on top left)
there is a choice called "Terrain"

While not a true USGS topo map, you get the idea.

 

[Scott Lurndal]

Andy Burns <usenet@andyburns.uk> writes:

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micky wrote:

Google doesn't have GPS devices at
any random location the user picks

Every user carrying a GPS enabled android device is crowd-sourcing data
for google, if someone's been there, google will know the altitude.

Nonsense.

 

[Bennett]

On 7/30/2019 11:43 AM, micky wrote:

When you use google maps to choose a route between two locations, and
choose walking or bicycling, it also shows starting and ending elevation
and a graph that shows changes, so you can see how many and how big the
hills are. Also useful, of course, just for finding elevation without
any walking.

But how does it know elevation. If a GPS gets signals from 3
satellites, it can calculate location, and if it gets signals from 4 of
them, it can calculate elevation. But the calculation is made in the
GPS device, such as a smartphone. Google doesn't have GPS devices at
any random location the user picks, and it has no way to read satellite
signals.

Is there some topographical map underlying the google maps, even though
there is no way to display that map wwithin google?

Just a guess that Google Maps could use elevation data from Google
Earth, (or its sources), which, according to this paper from 2017, makes
GE generally accurate:
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0175756

Apparently there are lots of accurate sources for elevation data.

 

[micky]

In alt.home.repair, on Tue, 30 Jul 2019 20:19:06 GMT,
scott@slp53.sl.home (Scott Lurndal) wrote:

Andy Burns <usenet@andyburns.uk> writes:
Thunderbird/60.8.0
In-Reply-To: <ho21ke161mdv4psg19j9u7silc99mt9alf@4ax.com
Content-Language: en-GB
X-Received-Bytes: 1151
X-Received-Body-CRC: 1553258581

micky wrote:

Google doesn't have GPS devices at
any random location the user picks

Every user carrying a GPS enabled android device is crowd-sourcing data
for google, if someone's been there, google will know the altitude.

That's a thought.

>Nonsense.

That's a thought, too!

BTW, I tried to use google walking to see how much elevation change
there was to the top of the next hill. I had thought the top of the
hill was the big street nearby, going along a crest (although crest
sounds more like a mountain than a hill.)

I found out, if it's at all correct, that's it's about halfway between
that big street and the next one aand that my elevation is about 400
feet. Typically, google directions gives three routes, and when I
changed to one of the others, it changed my elevation to 403 feet, even
though it was the same place.

It turns out I'm about 65 feet below the top of the ridge of hills a
half mile away. I think I don't get as much breeze as I would if I
were higher up. I'm not sure because I can't be in two places at once
and I spend comparitively little time farther up the hill. I like
living next to a stream, but not getting much breeze seems to be the
other side of the coin.

Does it seem correct to you that a mere 65' valley would be enough to
lessen the breeze I get?

 

[micky]

In alt.home.repair, on Tue, 30 Jul 2019 15:24:37 -0400,
"\"Retired"@home.com wrote:

On 7/30/19 2:43 PM, micky wrote:


Is there some topographical map underlying the google maps, even though
there is no way to display that map wwithin google?



If you click on the GMaps Menu icon (3 line "hamburger" on top left)
there is a choice called "Terrain"

While not a true USGS topo map, you get the idea.

Wow. I saw that years ago but I guess I forgot.

And that was just what I meant, a topographical map already ;inked to to
the street map.

I guess that answers the question.


Gfretwell said:

My guess is the Google Car that shoots all of the street view pictures
is using GPS to link the pictures to the map and they get the
elevation data at the same time.

That would make sense, and would be a lot easier than a lot of the
things they do.

Did you all know that besides the Google Car, there is now the Google
Man, who wears the camera a couple feet above his head, and they have
streetview pictures of some places one can only walk.

I think once I saw google pictures from a bicycle.


Thanks, all.

 

[rbowman]

On 07/30/2019 12:43 PM, micky wrote:

But how does it know elevation. If a GPS gets signals from 3
satellites, it can calculate location, and if it gets signals from 4 of
them, it can calculate elevation. But the calculation is made in the
GPS device, such as a smartphone. Google doesn't have GPS devices at
any random location the user picks, and it has no way to read satellite
signals

Probably LIDAR.

https://gisgeography.com/dem-dsm-dtm-differences/

https://gizmodo.com/google-has-its-own-fleet-of-airplanes-to-map-the-world-5916290

The gizmodo article talks about photographing for the 3D imagery but
while you're flying around might as well get the LIDAR data too.

 

[Jeff Liebermann]

On Tue, 30 Jul 2019 15:24:37 -0400, "\"Retired"@home.com wrote:

On 7/30/19 2:43 PM, micky wrote:
Is there some topographical map underlying the google maps, even though
there is no way to display that map wwithin google?

If you click on the GMaps Menu icon (3 line "hamburger" on top left)
there is a choice called "Terrain"

While not a true USGS topo map, you get the idea.

Yep. The basic numbers come from various elevation and terrain models
and databases. For example:
<https://www.usgs.gov/faqs/where-can-i-get-elevation-data?qt-news_science_products=7#qt-news_science_products>
<https://www.usgs.gov/core-science-systems/ngp/3dep/about-3dep-products-services>
<http://vterrain.org/Elevation/global.html>
<https://gisgeography.com/free-global-dem-data-sources/>
etc. There are ground level elevation maps, maps that include tree
and building heights for urban radio propagation studies, and maps
that include ocean bottom depths instead of ocean surface. There's
even a database of elevation databases:
<https://catalog.data.gov/dataset?tags=elevation>

For radio propagation studies, I use Radio Mobile software:
<http://www.ve2dbe.com/english1.html>
and SRTM (shuttle radar topography mission) 1 arc second (30 meter)
maps:
<https://www2.jpl.nasa.gov/srtm/>

I usually take the Radio Mobile maps, which show elevation,
<http://www.learnbydestroying.com/jeffl/coverage/VZW-water-plant/Picture11a.jpg>
and overlay them with the corresponding Google Earth map to produce
something like this cell site coverage map:
<http://www.learnbydestroying.com/jeffl/coverage/VZW-water-plant/Picture11a-google-earth.jpg>

The problem in not the lack of elevation maps, but rather an
overchoice of which one to use.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[whit3rd]

On Tuesday, July 30, 2019 at 11:43:32 AM UTC-7, micky wrote:

When you use google maps to choose a route between two locations, and
choose walking or bicycling, it also shows starting and ending elevation
and a graph that shows changes, so you can see how many and how big the
hills are. Also useful, of course, just for finding elevation without
any walking.

But how does it know elevation. If a GPS gets signals...

Elevation maps have been made before satellites, from aerial surveys; just the
change in position of objects with motion of a plane (flying a well-known path)
causes the successive images to show parallax. The resulting topographic
maps are widely available; orienteering wouldn't be possible without them.

 

[micky]

Another great discovery when clicking on the hamburger.

It has a line called streetview.

clicking that turns on all the streetview lines and dots, so that you
don't have to move Pegman each time you want to see one. You don't have
to use Pegman at all, just click on the location, and after you close
that window, the map with all streetview lines and dots will still be
there.

Did you all know that when a streetview on a line is open and there is
an arrow superimposed on the pavement, you can click on the arrow and
the next circular picture will be displayed, and maybe you can skip
ahead 2 or 3 pictures if you position the arrow farther away. This is
good when you're looking for the perfect view or something specific.


In alt.home.repair, on Tue, 30 Jul 2019 19:17:45 -0400, micky
<NONONOmisc07@bigfoot.com> wrote:

In alt.home.repair, on Tue, 30 Jul 2019 15:24:37 -0400,
"\"Retired"@home.com wrote:

On 7/30/19 2:43 PM, micky wrote:


Is there some topographical map underlying the google maps, even though
there is no way to display that map wwithin google?



If you click on the GMaps Menu icon (3 line "hamburger" on top left)
there is a choice called "Terrain"

While not a true USGS topo map, you get the idea.

Wow. I saw that years ago but I guess I forgot.

And that was just what I meant, a topographical map already ;inked to to
the street map.

I guess that answers the question.


Gfretwell said:
My guess is the Google Car that shoots all of the street view pictures
is using GPS to link the pictures to the map and they get the
elevation data at the same time.

That would make sense, and would be a lot easier than a lot of the
things they do.

Did you all know that besides the Google Car, there is now the Google
Man, who wears the camera a couple feet above his head, and they have
streetview pictures of some places one can only walk.

I think once I saw google pictures from a bicycle.


Thanks, all.

 

[Rob]

micky <NONONOmisc07@bigfoot.com> wrote:

When you use google maps to choose a route between two locations, and
choose walking or bicycling, it also shows starting and ending elevation
and a graph that shows changes, so you can see how many and how big the
hills are. Also useful, of course, just for finding elevation without
any walking.

But how does it know elevation. If a GPS gets signals from 3
satellites, it can calculate location, and if it gets signals from 4 of
them, it can calculate elevation. But the calculation is made in the
GPS device, such as a smartphone. Google doesn't have GPS devices at
any random location the user picks, and it has no way to read satellite
signals.

Google maps is not related to GPS!
Google maps is a MAP. A static piece of data that you can navigate.

When you have a map on paper (no idea how old you are and if you
have ever seen one), you don't ask "how can the map know this road
is here when it doesn't use GPS" either.

 

[Rob]

Andy Burns <usenet@andyburns.uk> wrote:

micky wrote:

Google doesn't have GPS devices at
any random location the user picks

Every user carrying a GPS enabled android device is crowd-sourcing data
for google, if someone's been there, google will know the altitude.

Google maps doesn't feed back user information into the maps, they
use existing survey data and also do their own surveys and photography.

The only feedback you see in the maps is the traffic info, obtained
by observing speed of users along roads.

 

[rbowman]

On 07/31/2019 03:06 AM, Rob wrote:

Google maps is not related to GPS!
Google maps is a MAP. A static piece of data that you can navigate.

When you have a map on paper (no idea how old you are and if you
have ever seen one), you don't ask "how can the map know this road
is here when it doesn't use GPS" either.

It's related so far as the rendered map is based on WGS84 and a
particular latitude and longitude relates to a number of tiles (png's)
depending on the zoom level.

Ultimately it relates to vector data that describes the road and is
rendered to produce the map tiles. The Google cars are collecting
photographic data but they are also collecting the GPS coordinates used
to build or update the vector data.

The photographic material is geotagged so it can be related to the
location. Mist smart phones and newer digital cameras do the same thing.
The EXIF data embedded in the image contains the location where the
photo was taken.

http://exifdata.com/

Note that is you run around taking selfies your camera or phone might
rat you out by putting you in a specific place at a specific time. The
same data allows you to position the photo accurately on a digital map.


Paper maps tended to do a lot of guessing.

 

[rbowman]

On 07/31/2019 03:08 AM, Rob wrote:

Google maps doesn't feed back user information into the maps, they
use existing survey data and also do their own surveys and photography.

https://support.google.com/maps/answer/3094088

Google does receive user input. OSM (Open Street Map) depends on user
input to a great extent although some information comes from publicly
available data like TIGER/Line in the US. Especially in Europe it can be
very accurate.

 

[Rob]

rbowman <bowman@montana.com> wrote:

On 07/31/2019 03:08 AM, Rob wrote:
Google maps doesn't feed back user information into the maps, they
use existing survey data and also do their own surveys and photography.

https://support.google.com/maps/answer/3094088

Google does receive user input. OSM (Open Street Map) depends on user
input to a great extent although some information comes from publicly
available data like TIGER/Line in the US. Especially in Europe it can be
very accurate.

This does not list "incorrect local terrain height" and also it is a
manual process for correcting errors. There is no such thing as a
feature in Google Maps that tracks your GPS position and reports it
back to Google for inclusion in the maps. The road information comes
from offcial (and their own) surveys, it is not like a road will be added
to the map when one or more Google Maps users cross a field somewhere.

And similarly, the local terrain height is not influenced by the height
indicated by users when they use Google Maps.

 

[Robert Roland]

On Tue, 30 Jul 2019 19:17:45 -0400, micky <NONONOmisc07@bigfoot.com>
wrote:

>I think once I saw google pictures from a bicycle.

They even use sheep these days:

https://visitfaroeislands.com/sheepview360/thanks-sheep-view-faroe-islands-now-google-street-view/
--
RoRo

 

[Clifford Heath]

On 31/7/19 9:17 am, micky wrote:

Did you all know that besides the Google Car, there is now the Google
Man, who wears the camera a couple feet above his head, and they have
streetview pictures of some places one can only walk.

Including inside some malls and department stores. I forget where I saw
that.