Author Topic: Google Maps: Overhead vs 45 deg views different dates??  (Read 517 times)

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M.C. Fujiwara

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Google Maps: Overhead vs 45 deg views different dates??
« on: January 18, 2013, 03:37:37 PM »
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I've been zooming around the Bay Area in Google Maps, gleaning ideas for the next Free-moN module  :scared: and I was looking around the Richmond Marina area where we participated in the GTE show last weekend.
Lot's o' good stuff.
During the show we watched a HUGE ship carrying some 4,000 Hondas pull into the auto-unloading dock across the water from Craneway Pavilion.
There were a bunch of autoracks lined up to receive the cars.

On Google Maps when you're not zoomed in all the way (before the angled view kicks in) it shows the tracks and autoracks:
http://goo.gl/maps/vyZuH

Yet when you zoom in a wee bit closer, the angled view kicks in and POOF! all the tracks and autoracks disappear as the map shows a images obviously taken before the tracks were put in:
http://goo.gl/maps/YMbHA

I've seen this happen a bit when zooming in to an earlier time period.
The image copywrite is all 2013.
Is there a way to find out the date of the different shots?
(Besides looking at the automobile models  :D)
M.C. Fujiwara
Silicon Valley Free-moN
http://sv-free-mon.org/

Dave Schneider

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Re: Google Maps: Overhead vs 45 deg views different dates??
« Reply #1 on: January 18, 2013, 04:23:17 PM »
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M.C.,

I don't know the specific answer to what Google is doing, but let me speculate with some professional experience in satellite and airborne remote sensing.
Although many refer to the images as "Google satellites", they (and others such as Bing) are just providing a visualization environment for commercial imagery sources. In the satellite world, these are primary Geoeye (http://www.geoeye.com/CorpSite/) and Digital Globe (http://www.digitalglobe.com/). There are many commercial airborne imagery providers as well. Both satellites and airborne sensors can shoot "straight down" (ie. at nadir) or at an oblique angle (off-nadir). 

For nadir shots, there is only one point in the image that is free of distortion (a over generalization, but lets not argue), which is directly beneath the sensor. Every other point will have some parallax in the image. This is seen most easily in tall objects which appear to lean away from the nadir point in all directions. The taller the object, the more the lean, and it gets to the point where you can see the side of the object facing the sensor, while the side away from it is hidden. IFor oblique images shot off-nadir, the affect is more pronounced, but offers some consistency as all the tall objects lean away from the sensor (not radiating out from the image center). 

Okay, if you are still with me, you must be interested. Satellites have an ascending orbit (from SE to NW) and a descending orbit (from NE to SW). Thus, those are the sides which can be viewed in an oblique many (like the Google 45). Airborne sensor are not constrained this way. The Bing maps oblique views typically show "more sides" of a building because they seem to utilize more airborne data and the aircraft can fly east-west and see the north and south sides of objects better. This is why you can rotate the viewing direction more readily in Bing than in Google Maps.

As for why the things go "poof" in Google, I speculate that they are using more of a nadir view for the zoomed out image and a more oblique view for the zoomed in portion because that view highlights the parallax  and makes it look more "3D". As for finding the dates, you might try looking in Google Earth using the timeline slider function. If you really need to know, you could do an archive search at Geoeye and Digital Globe, because that is probably where the images came from.

A long-winded answer to be sure, but that is how we roll on The Railwire!

Best wishes, Dave
If you lend someone $20, and never see that person again, it was probably worth it.

jagged ben

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Re: Google Maps: Overhead vs 45 deg views different dates??
« Reply #2 on: January 18, 2013, 04:48:37 PM »
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If you didn't know, you can toggle the 45 deg view in the upper right menu.  Also in some areas it is not available.

I have not figured out the date thing, but in almost every case I can recall, the 45 deg was older.


M.C. Fujiwara

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Re: Google Maps: Overhead vs 45 deg views different dates??
« Reply #3 on: January 18, 2013, 04:49:02 PM »
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Wow.
Thanks, Dave, for taking the time to type all that explanation out!
I knew that Google got it's info from other companies, but it's interesting to know about the various "uses" of satellites & planes.

I looked at the area in Google Earth and used the time traveler and saw the "close up" view (no tracks) in 2009, the "new" tracks in 2010, and the "now" view in 2011.
Very cool!
Even more cool: the 1939 version shows the curved trestle platform leading to the waterside of the Ford plant.

I had scrapped Google Earth a few years ago as it was slow & clumsy, but now I'm afraid I'll be spending too much time on it toggling through time!
I had been using the historic aerials site http://www.historicaerials.com/ which is pretty cool as well.
Thanks again!
M.C. Fujiwara
Silicon Valley Free-moN
http://sv-free-mon.org/

ljudice

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Re: Google Maps: Overhead vs 45 deg views different dates??
« Reply #4 on: January 18, 2013, 05:55:01 PM »
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Very interesting explanation!!!!!

Interesting, on BING, the "Bird's Eye" views of our house can be seen from four angles.  One of them was taken the day our buried oil tank was being removed!  The others came from a different day.

It was interesting to see a capture of a real event!

http://binged.it/XK94qk

- Lou

« Last Edit: January 18, 2013, 05:56:52 PM by ljudice »

Chris333

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Re: Google Maps: Overhead vs 45 deg views different dates??
« Reply #5 on: January 18, 2013, 06:01:24 PM »
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I bought my house 2 years ago. Google showed the old owners truck in the driveway. Then I built a back porch/deck and a month or two later the Google image changed to one with my porch.

I used to have Google Earth installed on my computer and it ran great. Now all Google maps does is freeze up on me. Bing works fine.

On my phone Google works fine and Bing doesn't work at all.   :?

davefoxx

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Re: Google Maps: Overhead vs 45 deg views different dates??
« Reply #6 on: January 18, 2013, 11:21:55 PM »
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I bought my house 2 years ago. Google showed the old owners truck in the driveway. Then I built a back porch/deck and a month or two later the Google image changed to one with my porch.

That's because Google knows what you're doing, so it sent a satellite overhead to record the remodeling.   ;)

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ljudice

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Re: Google Maps: Overhead vs 45 deg views different dates??
« Reply #7 on: January 19, 2013, 12:08:19 AM »
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OT, but sort of funny,  my sister who is completely non-technical was amazed by Google maps, Bing Birds Eye View, etc....
and especially webcams of the Garden State Parkway and other roads.

She called me the other day (from Florida) and asked me if I could see if see if a car was in her driveway in NJ.