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#183724 - 03/11/14 01:43 PM Google Maps
wandering_daisy Offline
member

Registered: 01/11/06
Posts: 2742
Loc: California
How do you find out the date of acquisition for satellite images used by Google Maps? It looks to me like they use a mix of several images taken at several different times. How often do they update? The reason I ask is that it looks like the Alpine Lake fire (2012 in the Wind Rivers) now shows up on the Google Maps. Hard to tell because the images are early season and there still is a lot of snow. It is a bit disappointing that some images of the highest areas are nothing but solid snow.

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#183726 - 03/11/14 02:10 PM Re: Google Maps [Re: wandering_daisy]
Rick_D Offline
member

Registered: 01/06/02
Posts: 2801
Loc: NorCal
Curious about that myself. Have never seen a published trick for decoding the date, so am left to sleuth and infer as to when an image might have been taken. Of course one of the big frustrations is when a mountainous area is photographed with a lovely snowpack--not uncommon.

I do a lot of A/B comparisons against Bing maps, which I frequently find better than the Google option in a given area.

Cheers,
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#183755 - 03/12/14 08:49 AM Re: Google Maps [Re: Rick_D]
Gershon Offline
member

Registered: 07/08/11
Posts: 1109
Loc: Colorado
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#183781 - 03/12/14 08:41 PM Re: Google Maps [Re: Gershon]
wandering_daisy Offline
member

Registered: 01/11/06
Posts: 2742
Loc: California
Thanks. I downloaded Google Earth. I was surprised at the wide range of image dates for one small area in the Wind Rivers - some from 1994 and some 2013. Part of the Alpine Lake fire shows up but unfortunately the upper edge of the fire area is on old maps. I think Google's focus on updated images is on urban and agricultural areas.

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#183783 - 03/12/14 09:08 PM Re: Google Maps [Re: wandering_daisy]
intrek38 Offline
member

Registered: 11/29/03
Posts: 430
Loc: Hesperia, Calif
I found 3 dates for the Sierra, as recent as 09-14-13. Take a look at how low Edison Lake was last summer.

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#183825 - 03/13/14 11:29 PM Re: Google Maps [Re: wandering_daisy]
phat Offline
Moderator

Registered: 06/24/07
Posts: 4107
Loc: Alberta, Canada

I've stopped trying to predict where they get updated images, particularly up here, with google earth.. Sometimes I find little tiny pieces of high definiton in a pile of low, etc - and with maps the pictures can change seasonally.
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#183877 - 03/16/14 02:22 AM Re: Google Maps [Re: phat]
billstephenson Offline
Moderator

Registered: 02/07/07
Posts: 3865
Loc: Ozark Mountains in SW Missouri
When they updated the photo of our place it was kind of shocking. I'd rather they did not provide anymore detail. They can get down to ants on the ground for public land, but they're too close already for private land.
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#183928 - 03/18/14 03:20 PM Re: Google Maps [Re: wandering_daisy]
GrumpyGord Offline
member

Registered: 01/05/02
Posts: 848
Loc: Michigan
I am not sure if I am doing something wrong or if Google maps and Google earth are really pretty useless in my area. I am in Michigan so most of the year the areas that I go to are either covered with snow or have heavy tree cover. For the most part the maps that I have looked at are no better than an aerial photograph taken far above the earth. They certainly do not even hint at a trail. Even major rivers do not show up well and small streams and springs do not show at all. Am I missing something or are the maps really useless. Operator error is certainly possible. Others seem to think that Google is great so it may be me.

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#183930 - 03/18/14 05:24 PM Re: Google Maps [Re: GrumpyGord]
BZH Offline
member

Registered: 01/26/11
Posts: 830
Loc: Torrance, CA
Well google maps and earth are nothing but photos taken from up high (I believe most are taken from airplanes). In many places they overlay trail maps on the photos though I doubt that is the case in many areas of Michigan. I've never been very successful trying to pick out trails off of google maps. I use a trail map for that.

I will add that bing usually has better (higher resolution) images for where my parents live in the UP.


Edited by BZH (03/18/14 05:25 PM)

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#183931 - 03/18/14 07:02 PM Re: Google Maps [Re: BZH]
wandering_daisy Offline
member

Registered: 01/11/06
Posts: 2742
Loc: California
Google maps are NOT just photos from high up. There are differences between air photos and satellite images. The "street views" may be photographic. For one thing a camera, even if digital, still collects the image through a lens. Satellites use large sensors that measure direct reflective energy. The farther "up" the more atmospheric distortion but you do not have lens distortion. The 3D images are made with two parallel passes to get the stereo effect. There is an incredible amount of image processing, complex map projection algorithms and tedious "ground truth" collected to get to an accurate end product. Google maps and Google Earth are not accurate end products that can be used for detailed navigation. They are nice 3-D pictures that are fun to view.

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#183940 - 03/18/14 11:11 PM Re: Google Maps [Re: wandering_daisy]
phat Offline
Moderator

Registered: 06/24/07
Posts: 4107
Loc: Alberta, Canada

I'll temper it a bit - if you're fortunate enough to have good high definition coverage of where you want to hike (the best I've ever had in a place i've hiked is tasmania - go figure) and you know how to look at a topo map, it's kind of nice to look at the terrain in conjunction with a reasonable contour map.

I'd certainly never plan a hike or a route only with that stuff though..
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#183949 - 03/19/14 06:10 AM Re: Google Maps [Re: phat]
GrumpyGord Offline
member

Registered: 01/05/02
Posts: 848
Loc: Michigan
OK I will have to look again but so far I think that the hype from folks who talk about using Google Earth to plan their hikes is a bit exaggerated. I think that a part of that may be the area I am hiking in. As I said it is mostly forest covered and being glacial moraine there are not a lot of elevation changes. Good old paper maps are more useful. Even forest service brochure maps beat aerial photos of the top of trees.

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#183954 - 03/19/14 08:58 AM Re: Google Maps [Re: GrumpyGord]
phat Offline
Moderator

Registered: 06/24/07
Posts: 4107
Loc: Alberta, Canada

If you`re used to air photos, and can get the infrared ones, (that are easy to distinguish the tree cover types on) they`re actually really good - but it takes some practice for looking at them in the context of the ground you`re walking over. I did this a lot in my youth, so I`m very comfortable with them.
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#183959 - 03/19/14 09:11 AM Re: Google Maps [Re: phat]
GrumpyGord Offline
member

Registered: 01/05/02
Posts: 848
Loc: Michigan
I think that there is some "operator error" involved here. Late yesterday afternoon I played around on Google Maps with an area I was thinking about hiking this spring and got true topo map with elevation etc. Today I go back to the same place and all I can get is the aerial view showing tree tops and terrain which is just shaded views. Elevation etc is grayed out and it says that it is not available for this area. Hard to believe that the information was dropped in the last 12 hours. So far my NG TOPO program is more useful but the Google information yesterday was more detailed but I do not know how to get back there.

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#183967 - 03/19/14 01:18 PM Re: Google Maps [Re: GrumpyGord]
BZH Offline
member

Registered: 01/26/11
Posts: 830
Loc: Torrance, CA
Topographical line on Google maps are only available at certain zoom levels. Try zooming in or out.

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#183969 - 03/19/14 02:00 PM Re: Google Maps [Re: BZH]
Rick_D Offline
member

Registered: 01/06/02
Posts: 2801
Loc: NorCal
Originally Posted By BZH
Topographical line on Google maps are only available at certain zoom levels. Try zooming in or out.

I don't actually see traditional topo maps but rather, "terrain" view, which is simulated 3-D combined with contouring. Like you note, it's not available at the highest zoom levels, so zoom out until the option appears.

Repeating myself from earlier, for areas where Google is not providing useful maps/images, check the Bing equivalent. It's often better.

Cheers,


Edited by Rick_D (03/19/14 02:02 PM)
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#183970 - 03/19/14 02:06 PM Re: Google Maps [Re: BZH]
GrumpyGord Offline
member

Registered: 01/05/02
Posts: 848
Loc: Michigan
I tried zoom in/out and I can only get elevation lines at zoomed way out. Yesterday I was getting a much closer view with elevation lines. Today it says "lite Mode". Not sure about yesterday. It says that if I can only use lite mode I should check to make sure that my OS, browser and video driver is up to date. They are up to date. I don't know what was different yesterday. Last night I was thinking that it was something I might be able to use.

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#183979 - 03/19/14 10:14 PM Re: Google Maps [Re: GrumpyGord]
phat Offline
Moderator

Registered: 06/24/07
Posts: 4107
Loc: Alberta, Canada

Yeah it`s lovely way of switching stuff around to `help` you is kind of annoying -

To force it to the non-lite mode try hitting https://www.google.com/maps/preview/?force=webgl
instead of going to the default url (maps.google.com)

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#184002 - 03/20/14 05:59 AM Re: Google Maps [Re: phat]
GrumpyGord Offline
member

Registered: 01/05/02
Posts: 848
Loc: Michigan
Phat: Still says sorry only lite mode is available at this time. I wonder if Google is having some type of problem.

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#184003 - 03/20/14 07:40 AM Re: Google Maps [Re: GrumpyGord]
phat Offline
Moderator

Registered: 06/24/07
Posts: 4107
Loc: Alberta, Canada
That's very possible, or something in your computer or browser is preventing the webgl stuff from running. (security settings in your browser maybe?)
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#184022 - 03/21/14 05:32 PM Re: Google Maps [Re: wandering_daisy]
billstephenson Offline
Moderator

Registered: 02/07/07
Posts: 3865
Loc: Ozark Mountains in SW Missouri
That's very good info W_D.

While I think Google Maps can be a useful tool to help plan a trip I mostly use them to review one.

I guess Google's "Shaded Terrain" maps prove I'm right brained because they look inside out to me (i.e. the valleys look like mountains and vice/versa). Hard as I try I can't reverse that so they are nearly useless to me.

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"You want to go where?"



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#184160 - 03/29/14 03:57 AM Re: Google Maps [Re: billstephenson]
TomD Offline
Moderator

Registered: 10/30/03
Posts: 4963
Loc: Marina del Rey,CA
At the risk of sounding like a wise ***, if you Google "how are Google maps made" and similar search terms, all sorts of articles pop up explaining how the maps are made, how to decode the photos, etc. The Atlantic has one that gives an "inside" look at how they make maps. Most of that info applies to urban areas, though. But it does give you an idea as to what they are up to.

Here is some interesting info from a few years ago.
Google info


Edited by TomD (03/29/14 04:04 AM)
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#184168 - 03/29/14 05:24 PM Re: Google Maps [Re: TomD]
wandering_daisy Offline
member

Registered: 01/11/06
Posts: 2742
Loc: California
I read that stuff - still does not get to the heart of overlaying data into one map. The earth is round, maps are flat. Not all data layers use the same map projection. Any photographic data has lens distortion. Also all digital data has its smallest unit - not all digital data units are equal size. And then there are those pesky shadows.

Layering all that data actually creates phantom data. There are lots of people working on lots of methods to make the process more accurate. Google's "human" input with an army of people with I-phones or whatever, improves accuracy where there are hundreds of people. I am mighty glad there are not hundreds of people in each square mile in the wilderness! The accuracy of google earth in the wilderness vs cities is vastly less. I have spent many hours looking at google earth maps in area where I have traveled and although pretty good, it still does not equal a geo-referenced stereo pair of low altitude air photos. We used those eons ago even in the 1970's to make geologic maps. BUT, the air photo was just the base map - we walked every inch of every geologic unit boundary and plotted on the map. That is "ground truth". Seldom can I find on google earth, the off-trail route that I took. A 10-foot cliff may stop you cold, but not show up on google earth.

A few good things though. With the date of the data, I found out that a stream I was hoping to walk down was bone dry on the October 2012 photo! Not that there are not small pockets of water, but it gave me a "heads up".

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#184195 - 03/31/14 03:42 AM Re: Google Maps [Re: wandering_daisy]
TomD Offline
Moderator

Registered: 10/30/03
Posts: 4963
Loc: Marina del Rey,CA
I would bet with the drought out here, that many of the streams that show up on maps or old photos are dried up, even with the bit of rain we've had. Some of the big lakes that are used for irrigation or drinking water, like Folsom, East of Sacramento are practically empty.
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