From: Ronald Wong (ronwong@inreach.com)
Date: Wed Oct 10 2001 - 16:41:30 PDT
Message-Id: <l03102800b7e7cf5f2e09@[209.209.20.50]> Date: Wed, 10 Oct 2001 16:41:30 -0700 From: Ronald Wong <ronwong@inreach.com> Subject: re: Cities from Space
Raleigh McLemore said:
>The Oakland School District has a map site that allows
>you to see aerial photography of our city and schools.
>You can "zoom" closer or farther, showing more or less
>of the map. At the closest range you can almost see
>people and make out car types. There is a scale
>offered with each change in "your altitude", such as,
>1" equals 60' or 1" equals 1000'...
>... but the maps are only of Oakland.
If you go to: http://earth.jsc.nasa.gov/city.html, the website of NASA's
Johnson Space Center, you'll be able to download aerial images of many
cities around the world. These can be saved and examined using any viewer,
draw/paint program, or photo editor that you may happen to have on hand.
With these tools, you can zoom in and out to your heart's content.
Unfortunately, to have the resolution that will allow you to do what
Raleigh did, you need to download the HIGH resolution images at this
website. These images can be as big as 75 megabytes when uncompressed. If
all you have is a 56.6K modem, this means HOURS of download time.
If you'd like to try playing around with these images, I'd suggest that you
do the download at your school site. It probably has at least a T1
connection with the internet and the download should take considerable less
time - relatively speaking.
Unlike his image of Oakland, there is no scale supplied with these images
so you'll have to use the known dimensions of an object in the picture to
determine the scale.
While you're at this JSC's website, I'd suggest you poke around and find
out what else is there. This webpage is part of a larger offering that was
set up with teachers in mind so you may find some resources there that are
very useful to you and your program.
Raleigh asked:
> Can I take the map and scale to determine the approximate
> height of the view? Can I tell my younger kids "This
> picture is how the school looks if you are a bird flying
> 100' above us, or a 1,000 feet above us"?
Yes.
If you are 6 feet tall and someone 3 ft. tall is looking at you from 3 ft.
away your figure will subtend an angle of about 90° (if his/her eyes were
at the top of his/her head and the two of you were as thin as a line, it
would BE 90°).
If they were looking at a photograph of you and moved it towards/away from
themselves until your figure subtended an angle of 90° then, at that
moment, they would be seeing you as if they were 3 feet away from you.
It's simply a matter of geometry.
If someone was at an altitude of 500 ft. above the center of a line 1000'
in length drawn on a street in Oakland, they would see that the line
subtends an angle of 90°.
Measure the length of the scale for Oakland on the screen of you monitor.
Let's say it turns out to be 20 cm. Then, if your students position their
eyes 10 cm from the screen, they will be viewing the scene as if they were
half the scale above the scene. If this scale happens to be for 1000 feet,
then they will be viewing the scene as if they were at an altitude of 500
feet.
What about other multiples of the scale - Like elevations equal to the
scale or greater? Well, since everything is drawn to scale, the ratios of
the distances in the real world are the same as that for the world of the
map. So, if your students view the map at a distance EQUAL to the length of
the scale as it appears on the screen, they will be viewing the scene at an
altitude equal to the map's scale and multiples of this particular distance
will be multiples of the scale.
If you simply multiply the scale on the screen by the ratio of the average
viewing distance from the monitor to the length of the scale on the
monitor, you'll have the average elevation at which they are viewing the
scene. This may be all that you need to know.
Cheers - ron
This archive was generated by hypermail 2.1.3 : Mon Aug 05 2002 - 09:21:36 PDT