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www.terraserver.microsoft.com
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Recently we came across a web site that could be
described as the world’s greatest site – in the
true sense of the word great, that is.
www.terraserver.microsoft.com is, without doubt,
the world’s largest site and its contents could
truly be described as “out of this world”.
With more than 1.2TB of data,
TerraServer contains more data
than all the HTML pages on the web
combined.
Hang on a minute, what’s a TB?
You’ve heard of megabytes (most web
sites are less than 1MB). Next up the
scale is the gigabyte (GB), or 1,000MB.
A terabyte, TB, is 1,000,000MB or
1,000,000,000,000 bytes. That's equivalent to about a billion pages of text
or four million books. Whew!
What occupies this mind-boggling
storage space? Thousands upon thousands of black and white photographs
of the Earth, taken from one of two
satellites over the past decade or so.
One of those satellites is courtesy of
the United States Geological Survey
and the other is from the Russian
Space Agency, Sovinformsputnik.
The US satellite has concentrated
mainly on the United States, while
the Russians are responsible for
most of the rest of the world. While
most populated areas of the US are
covered, the rest of the world is someMAY 1999 3
MAY 1999 3
You can point and click to anywhere on the world map
shaded in green (we've enlarged the map of Australia to
show the areas that aren't covered). The area under the
map allows you to select a number of famous places.
what less represented – and patchy.
In Australia, Melbourne, Brisbane
and Perth are all covered but for some
reason, the centre of the Universe
(Sydney, to those living in it) is not.
Melbourne, Brisbane and Perth readers are probably saying “rightly so!”
Enough frivolity: let’s get back to
TerraServer. By a happy coincidence
(?), tera not only means 1012, add
another “r” and you have the Latin
word for earth.
The surface area of the Earth is
about 500 square terametres (there’s
that word again!), of which about
100 are dry land. Of that, only about
four square terametres are populated,
the rest being mountain, desert, ice
capped, farmland and so on.
The Soviets have so far managed to
photograph about two square tera-metres, or about half of the populated
area. While some of the information
is getting a little dated (Melbourne, for
example, was photographed in 1991),
it is still a valuable source of information for a huge variety of people. The
Soviet images, by the way, are called
SPIN-2, a reference to that two square
terabytes.
Or you search for a city/area and see if it is covered. The
two columns on the right show the images from the US
(left) and Russian (right) satellites. Point and click on
either to load the respective image.
virtually seamless precision.
Those 16 photos will give you a base
resolution of 16m to the centimetre.
Click on an area of the photograph and
the next resolution will load, this time
at 8 to the centimetre. The highest resolution depends on the source of the
photos: the US satellite pics are at the
incredible resolution of 1m per pixel.
That’s enough to pick out individual cars on a roadway but not, as you
might have seen in spy movies, read
their number plates or view the driver.
Incidentally, such resolution, in real
time, is believed to be possible from
many of the spy satellites now in use.
Number plates with their 100mm high
letters are said to be a doddle.
Fairly believable reports state that
today’s spy satellites are good enough
to pick up the dateline on the front of
a newspaper (usually about 12-14pt
type) while less believable rumours
state that the latest generation of spy
satellites can actually read the news-
How does it work?
When you access the TerraServer
web site, you are presented with a
map of the world with photographed
areas coloured green.
Click on any of these areas and the
photographs for that area begin to
download. When we say photographs,
we mean just that: up to 16 photographs are assembled on screen with
4 Silicon Chip
Melbourne's CBD as loaded from TerraServer. This is the lowest resolution image
but even this is more than adequate to easily spot major landmarks – Docklands,
the Yarra and the MCG, for example. We've also chosen the lowest size – this
could be increased to full screen with the buttons on the left side of the screen.
This montage covers roughly Ascot Vale in the top left to Richmond bottom right.
paper itself (usually 7 or 8pt type!)
But we digress – again.
The resolution from the Russian-sourced photos is not quite as
good; they are at 1.56 metres per pixel.
More importantly, though, if you want
to view hi-res images from the Russian
source, you have to pay for them.
But we imagine that most people
using the site will be more than happy
viewing the on-screen images (free).
Hey, look, there’s our house. . .
Terabytes of storage
To hold, access and download
Terabytes of information you might
expect a system that’s a bit more than
an old AT with a big hard disc. And
you’d be right!
The TerraServer system runs on a
Digital Alpha 8400 system with eight
(yes, 8) 440MHz Digital Alpha processors and a massive ten gigabytes
(10GB) of memory (yes, memory!).
The machine is connected to seven
dual-ported Ultra-SCSI host-bus adaptors, each of which interfaces with a
disc drive cabinet containing 46 nine
gigabyte drives.
Quickly doing a bit of mental
arithmetic, 7 x 46 is 322 drives, plus
the couple in the Digital Alpha 8400
– means a system with 324 drives
totalling 2.9TB of storage. Using a
RAID (redundant array of independent
discs) setup, the drives are configured
to act as four logical drives of 595GB
each.
SQL Server Enterprise Edition
stripes the database across the four
logical volume. After taking the
data-management overhead into account, the array has about 2.4TB of
storage capacity. And if something
goes wrong, there’s a tape back-up
which can handle 5TB of data.
The system runs on Microsoft NT
Server V4.0 with SQL Server, already
mentioned.
Here is the Brisbane
CBD and inner west,
photographed from
space courtesy of the
Russian satellite. This
covers an area from
about The Gap top left
through to Kangaroo Pt
in the bottom right. The
white lines in the centre
of this pic are where the
joins between frames
(automatically done
on download) were not
quite seamless.
Enlarging up one step
we find the CBD coming
more clearly into view,
along with the bridges
over the Brisbane River.
Note the shadow cast by
the Story Bridge (right
side) – obviously an
early morning photograph. The advert (top
right) helps pay for the
site so it’s free for you to
browse.
We’ve enlarged again but
this time also selected the
larger view. We're
looking here at Brisbane
City, with the Roma
Street station and goods
yard along with the
Brisbane River bottom
left. At this scale you can
start to pick out vehicles
on the bridge and rail
wagons.
Who pays for it all?
Love ’em or loathe ’em, you have to
take your hat off to the people at Microsoft for getting behind this project.
While the site is also supported by
on-screen adverts (not too intrusive,
as you’ll see from the screen grabs), it
would appear that Mr Gates and his
team are the money behind it.
Of course, this is also an excellent
advertisement for Microsoft and its
operating system: if it can handle the
world’s largest website 24 hours a day,
Enlarged yet again to
the highest resolution,
this time back on the
eastern City with the
Story Bridge/Kangaroo
Point on the right.
Note the grey patches
middle and lower left
– these are glitches in
the system which can
sometimes be removed
by refreshing the screen.
MAY 1999 5
By way of contrast, here is an image
of the San Francisco Fisherman's
Wharf area, taken from the USGS
satellite. There’s not a huge amount to
choose from in this screen image but
remember you can download a hi-res
image of any of the USGS files free of
charge. The Russian SPIN-2 images
are also available but you have to pay
for them!
such as this, we want to use a system
typical of that which most readers
would have (we were using a midrange 486 with a pretty good graphics
card and a fast [56K] modem). One of
these days we’ll give it a fly on a fast
Pentium II machine with heaps more
“grunt” just to see how it goes.
Obtaining images
seven days a week, think how easy
your system will work. . . Naturally,
accessing Microsoft’s MSN is only a
click away from the site, too.
Others supporting the venture are
Compaq, Storageworks and Storagetek.
Once loaded, you can also move in
any direction from that photo to the
next (we have difficulty not calling
them maps, but they are real photos)
by clicking on any of the eight green
arrow buttons around the edge of the
pic.
Accessing images
But wait, there’s more!
We’ve described how easy it is to
“point and click” to obtain any area
on Earth. But there’s more than one
way to skin a dead cat, so to speak.
You can also type a place name into
the system’s search engine and it will
find ALL places on Earth with that
name. (Bet you didn’t know that there
are 16 Sydneys, did you?).
If the location is on the database,
alongside it will be one or two clickable filenames. One column lists the
USGS images, the second the Russian
images. If the name is present, clicking has the same effect as clicking
a location on the world map. When
it loads, the name of the location is
shown above the photo image.
In fact, the name may be much
more localised than you asked for:
we loaded Brisbane by clicking on it,
zoomed in and found that the name
had changed to Petrie Terrace. Sure
enough, our image showed the Brisbane suburb of Petrie Terrace!
You don’t have to search for just a
location, either: a pull-down menu lets
you specify a qualifier such as river,
bay, airport and so on.
There are also images of famous
places to view (mainly US, of course),
many in superb resolution. But where
is the Sydney Opera House or the
Coathanger?
As you might expect, the site is
continually evolving and will – hopefully – contain many more areas in the
not-to-distant future.
A couple of negative comments,
though: downloading huge files
(which is what you are doing) takes
a significant amount of time. And the
system is by no means perfect – we
found several times that one frame out
of 16 simply refused to load; or one,
perhaps two frames were corrupted,
with “holes” in them or areas not
appearing.
Sometimes, the seams between adjacent frames did not quite work and
a thin white line appeared.
And sometimes, frames simply refuse to load. In many cases, hitting the
“refresh” tab cleared these problems,
but not always.
It is more than possible that some of
the limitations in the system were at
our end. But whenever we do reports
6 Silicon Chip
The vast majority of web surfers
would simply visit the site to view
places of interest. But if you want to
obtain hi-res images, you can. If they
are from the USGS satellite you can
download them free of charge.
The Russian images, though, will
cost you (they’re actually provided
by an American supplier – good ol’
capitalism strikes again!). Details are
provided on the web site.
If you get the impression that we’re
pretty impressed with www.terraserver.microsoft.com, you’re spot on.
Not just because of its awesome
size and power; not just because it’s
a site which will interest everybody;
not just because it’s a technological
breakthrough; not just because of its
ease-of-use and, to use a hackneyed
term these days, “user friendliness”.
We’re also mightily impressed that,
even if the technology to do all this
was available a decade or so ago (it
wasn’t!), can you imagine the Russians
allowing Americans access to what
would be (then) a top-secret photo
library and then make it available to
the world?
Let’s just hope the spirit of cooperation which has seen this site evolve
can find its way into other areas of
technology.
SC
Acknowledgement:
Much of the technical information in this
article first appeared in the US magazine, Popular Electronics, March 1999.
Screen grabs courtesy of www.terraserver.microsoft.com
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