3 ms·

> You can pretty much get a 3d map of the world with 5m accuracy ( Related, maybe OT, but you seem a person that knows a lot more about this than I would know:

> You can pretty much get a 3d map of the world with 5m accuracy ( Related, maybe OT, but you seem a person that knows a lot more about this than I would know: more exactly I wanted to ask you if you know of a decent enough method to get the height of a building based on GoogleStreetView. Meaning, I'm "inside" GoogleStreetView, I'm looking at a "building" from outside on the street, I know the geo coordinates of the camera that took the photo, I know the geo coordinates of the building, so that I know the distance between the photo camera and the building, I can "count" (for lack of a better word) the building's size in screen pixels (or some other unit/reference? which one?), and based on all that I'm curious if one can get the real height in meters of said building. From what I could found around on some other forums there were people mentioning the aperture of the GoogleStreetView photo camera being part of the "equation" to compute it all, and that would be a problem because we do not know the values for the aperture. I have no idea though if all that discussion was on the subject or not.

Waterluvian 4y ago
The images need to be rectified or else, yes, the lens distortion messes up the measurements. Really you just need a length and an angle to complete the triangle. The length is easy: measure distance from base of building to any point where you know the angle. But getting the angle from a point to the top of the building is tricky. I don’t know if any clever way to estimate that without stereo imagery. A lot of this stuff is automatically calculated when a digital surface model (DSM) is generated from stereo pairs of images. So you might be able to just look it up in Google Earth. This is the data (probably blended with many other sources such as LiDAR and ground survey data) Google uses to extrude buildings into 3D models. P.S. this was an assignment in 1st year for me. Estimate the height of the CN Tower from some aerial photos. I feel like I should remember more.
sorenjan 4y ago
I took a shot at this. If you assume flat terrain between you and the base of the building, the problem can be simplified to basically the distance to the building from your current position times the tangent of the angle from the horizontal plane to the top of the building, from the definition of the tangent function[0]. To find the distance you can plug in your current coordinates and the buildings coordinates in a great circle distance calculator, like this one: [1], or just use the distance measure feature in Google maps. To find the angle you can zoom in on the top of the building in street view mode, and in the URL you'll have the pitch angle as a number between 1 and 179, ending in t [2] (so for instance 150.1t is a pitch angle of 150.1 degrees). Conveniently you'll also have the coordinates of the street view position in the same URL. To get the angle from the horizontal plane you have to subtract 90, since 0 pitch is straight down. I tried it with a tall building (Turning Torso in Malmö), and got 199 m on my first attempt and 195 on my second. The correct height is 190.4 m, so pretty close. The first attempt was 100 m away, the second more than 1.2 km. I then tried it with the Chrysler building from the other side of East river about 1.5 km away, and got 274 m which is close to the actual 282 m. You can probably use more sophisticated methods that downloads the 360 image as a stereographic projection and extracts the pitch angle from there, but for something that's a close enough one off I think this works ok. [0] https://en.wikipedia.org/wiki/Trigonometric_functions#Right-angled_triangle_definitions https://en.wikipedia.org/wiki/Trigonometric_functions#Right-... [1] https://www.gpsvisualizer.com/calculators https://www.gpsvisualizer.com/calculators [2] https://www.trekview.org/blog/2020/decoding-google-street-view-urls/ https://www.trekview.org/blog/2020/decoding-google-street-vi...

Waterluvian 4y ago

The images need to be rectified or else, yes, the lens distortion messes up the measurements. Really you just need a length and an angle to complete the triangle. The length is easy: measure distance from base of building to any point where you know the angle. But getting the angle from a point to the top of the building is tricky. I don’t know if any clever way to estimate that without stereo imagery. A lot of this stuff is automatically calculated when a digital surface model (DSM) is generated from stereo pairs of images. So you might be able to just look it up in Google Earth. This is the data (probably blended with many other sources such as LiDAR and ground survey data) Google uses to extrude buildings into 3D models. P.S. this was an assignment in 1st year for me. Estimate the height of the CN Tower from some aerial photos. I feel like I should remember more.

sorenjan 4y ago

I took a shot at this. If you assume flat terrain between you and the base of the building, the problem can be simplified to basically the distance to the building from your current position times the tangent of the angle from the horizontal plane to the top of the building, from the definition of the tangent function[0]. To find the distance you can plug in your current coordinates and the buildings coordinates in a great circle distance calculator, like this one: [1], or just use the distance measure feature in Google maps. To find the angle you can zoom in on the top of the building in street view mode, and in the URL you'll have the pitch angle as a number between 1 and 179, ending in t [2] (so for instance 150.1t is a pitch angle of 150.1 degrees). Conveniently you'll also have the coordinates of the street view position in the same URL. To get the angle from the horizontal plane you have to subtract 90, since 0 pitch is straight down. I tried it with a tall building (Turning Torso in Malmö), and got 199 m on my first attempt and 195 on my second. The correct height is 190.4 m, so pretty close. The first attempt was 100 m away, the second more than 1.2 km. I then tried it with the Chrysler building from the other side of East river about 1.5 km away, and got 274 m which is close to the actual 282 m. You can probably use more sophisticated methods that downloads the 360 image as a stereographic projection and extracts the pitch angle from there, but for something that's a close enough one off I think this works ok. [0] https://en.wikipedia.org/wiki/Trigonometric_functions#Right-angled_triangle_definitions https://en.wikipedia.org/wiki/Trigonometric_functions#Right-... [1] https://www.gpsvisualizer.com/calculators https://www.gpsvisualizer.com/calculators [2] https://www.trekview.org/blog/2020/decoding-google-street-view-urls/ https://www.trekview.org/blog/2020/decoding-google-street-vi...