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Old March 26th, 2007, 07:41 PM   #1
Tom_Green
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How tall is a skyscraper? My method for everyboddy to find it out ;)

At first i have to admit that my method doesn`t work everywhere. The city must be on flat land. Sorry Hong Kong.

What else do you need? A skyscraper where you know the height and google earth.

My method:
You need to find a place where both skyscraper have the same "height"

My example is the spire of the Maintower and the spire of the Commerzbank Zentrale.


You need to remember where you have taken the pic.


Now you need google earth. Find the place and find out what`s the difference is between the 2 towers and the difference between you and the first tower.

In my example is the difference between the Main Tower and the Commerzbank Tower is 197,1m and between me and the Main Tower is the difference 862,69. The difference between me and the Commerzbank is 1059,79m.


Now some math. I know that the spire of the Main Tower is 240m above the ground.

240m:862,69*1059,79=294,83m
So i calculated the height of the Commerzbank Tower with 294,83m. The real height is 299m. Not bad because the land is not 100% that flat.

Now to something more interesting, the Burj Dubai.

Altin took this pic (look at Burj Dubai and the 21st Century Tower 269m)
[IMG]http://i3.************/2qducrl.jpg[/IMG]

from that position.
[IMG]http://i11.************/4bdzwar.jpg[/IMG]


My calculation for the Burj Dubai:
269:2645,2*4184,5= 425m

If you do this by yourself, don`t forget that you`r eyes are not on the ground level.
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Old March 26th, 2007, 07:52 PM   #2
ZZ-II
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not bad tom, but we should make more such calculations to get sure!
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Old March 26th, 2007, 07:53 PM   #3
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nice way, bravo

seems high in accuracy 4 flat land
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Old March 26th, 2007, 07:57 PM   #4
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Quote:
Originally Posted by ZZ-II View Post
not bad tom, but we should make more such calculations to get sure!
I tried it several times and it`s very accurate. But i will do this during my trip in Dubai. I will use 3 towers to be more accurate.
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Old March 26th, 2007, 08:12 PM   #5
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It might even work if the city is not totally flat, as Google Earth gives you the elevation for every point. I donīt know if the elevations at Google Earth are accurate enough though.

Another way might be measuring the shadow of the building, if you have the formula for the exact angle of the sun at a given time and date.
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Old March 26th, 2007, 08:20 PM   #6
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Martin, I'M SORRY.

I totally screwed up the location (or better say orientation). Here's the correct point:

[IMG]http://i12.************/2cfsems.jpg[/IMG]
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Old March 26th, 2007, 08:55 PM   #7
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Quote:
Originally Posted by Tom_Green View Post
I tried it several times and it`s very accurate. But i will do this during my trip in Dubai. I will use 3 towers to be more accurate.
It is just the same with GPS systems like US GPS, Glanoss(Russian) etc...
The more sattelites the more precision you get so i advise to use 4 buildings instead off 3.

Some beer for you my skyscraper brother you deserved it.
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Old March 26th, 2007, 09:10 PM   #8
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like i got time for this. i have better things to do.
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Old March 26th, 2007, 09:13 PM   #9
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Thanks Tom_Green . I know a similar way to measure heights, it is basically same and is using same formula. Only difference is that I'm using shadows. This method is very old and was used in ancient Egypt to measure the height of the pyramids (can't remember correctly).

Here is how it works (look at the picture). First of all measure the object's shadow (A). Now stand in tip of the object's shadow and measure the lenght of your shadow (B). (Alternatively you can use some stick and measure it's shadow length) Next multiply the length of the object’s shadow by your height (C) and then divide the result by the length of your shadow (B) and you should have pretty accurate result.

I hope this is accurate method too, I only use this method to measure tree height

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Old March 26th, 2007, 09:54 PM   #10
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Thanks for your comments.

Altin: No problem

Okay the new position
[IMG]http://i12.************/2cfsems.jpg[/IMG]

269:2707*4246= 421m.

Quote:
Originally Posted by european View Post
like i got time for this. i have better things to do.
like posting in this thread
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Last edited by Tom_Green; March 26th, 2007 at 11:34 PM.
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Old March 26th, 2007, 10:39 PM   #11
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Very useful method, thank you a lot, il make sure to try it out later .
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Old March 27th, 2007, 11:28 PM   #12
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Dhyaffa is slightly higher than burj dubai, probably 5-6 metres.

it is a sandbank, and burjdubai is on an ancient creekbed.

i dont know how that effects your calculations if it does at all...
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Old March 28th, 2007, 01:00 AM   #13
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Quote:
Originally Posted by Twipsy View Post
It might even work if the city is not totally flat, as Google Earth gives you the elevation for every point. I donīt know if the elevations at Google Earth are accurate enough though.

Another way might be measuring the shadow of the building, if you have the formula for the exact angle of the sun at a given time and date.
heights given on google earth are way out! i think everyone knows that. dont you?
i have height maps for sydney and otehr locations and i compare to google earth and there always 30-40m out . why is google earth hopeless when i tcomes to elevation?
Its distances seem to be very accurate though.
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Old March 28th, 2007, 02:11 AM   #14
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So what u do is finding out the tangens of the angle of view to the both buildings in a streight line.
So u get a simple linear equation like in 8th grade @ school.
yah this method must be really accurate. there can hardly be any mistake. only mistake u can make is choosing the wrong position in google earth because resolution at some spots is too low for very accurate location of position.


Last edited by idkblk; March 28th, 2007 at 02:17 AM.
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Old March 28th, 2007, 02:31 AM   #15
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Quote:
Originally Posted by idkblk View Post
only mistake u can make is choosing the wrong position in google earth because resolution at some spots is too low for very accurate location of position.
Fortunately, Dubai is not one of those places, as the whole city is at least 1m/pixel resolution.

The basemap for Google Earth is 15m/pixel so in places that don't have supplementary high resolution data it wouldn't work. I'm looking forward to Tom_Green's results.
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Old March 28th, 2007, 09:10 AM   #16
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Don't forget to account for the curvature of the earth at great distances
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Old March 28th, 2007, 08:18 PM   #17
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Yah you are right. But the Effect in Distance you use for that (between 3 and 5 km) isnt too high.
Anyways, it makes the calculation more complicated and the result wont have much better accurancy because the failure in detecting the very correct angle just by eye has a much higher influence on the accurancy. Not to mention the diversity of the ground levels.
You can see the height above ocan on google earth, but the resolution of that is not good.
in my area google earth has also good resolution in image, but not of terrain height.
there is a cliff next going about 40 meters rectangle in the air. but terrain in google just shows "smooth" terrain.
And for building roads and so on, the point where u stand they often elevate the groundlevel some meters so u can not detect too simple the accurate difference of groundlevels at your and the burj site so.. like i said including earth curvature is to break a butterfly on a wheel

Last edited by idkblk; March 28th, 2007 at 08:24 PM.
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Old March 28th, 2007, 08:39 PM   #18
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Quote:
Originally Posted by idkblk View Post
So what u do is finding out the tangens of the angle of view to the both buildings in a streight line.
So u get a simple linear equation like in 8th grade @ school.
yah this method must be really accurate. there can hardly be any mistake. only mistake u can make is choosing the wrong position in google earth because resolution at some spots is too low for very accurate location of position.

Let`s take this into account.
Altin took the pic from a car so he was around 1m above ground.
I hope you will undertsand this as it`s difficult for me to describe
1:269*2707=10m
2692707+10)*(4246+10)= 421m.
Not much changed.

Quote:
Originally Posted by DUBAI View Post
Dhyaffa is slightly higher than burj dubai, probably 5-6 metres.

it is a sandbank, and burjdubai is on an ancient creekbed.

i dont know how that effects your calculations if it does at all...

Let`s also take this into account.
(269+6):2717*4256=430m
This changes alot.

But if you say that the position where you took the pic is 3m lower as the base of the 21st century tower you have to change it again.
3m:269*2707=30m
275:2747*4286=429m

But letīs be honest.I need to be there and i need more towers for the calculation. I will aslo use my 300mm lens for the pics. I hope it will works.
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Old March 29th, 2007, 12:59 AM   #19
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im going to try your method at lunch time in sydney today. i know all heights of every building in the city so ill takes some dif shots lining up various bldgs. ill try to get same height of land between each tower but sydney is quite hilly not flat so may prove hard.ill post my findings
cheers
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Old March 29th, 2007, 02:59 AM   #20
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This method is really smart, idkblk. But to get an idea of the accuracy, do a test with a building of unknown height and measure it using as many buildings of known height you can find. Then calculate the average and standard deviation. The latter number gives you an idea of the accuracy.
Alternatively, you can also test it on many buildings of known height. Or would someone else take up this challenge? Success!
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