How To Use Satellite Technology To Develop The Simulation Environment

By Jamie Al-Nasir

Introduction/Article Overview

his article serves to briefly demonstrate the use of satellite imagery in the development of flight simulation scenery. Nowadays the images produced by what is effectively a giant (and expensive) camera flying in orbit 423 miles earth at almost 17500 miles per hour is truly amazing - not just your average Kodak!

IKONOS satellite image of Jacobabad Air field. © Space Imaging Corp.

Aerial snapshot of the actual scenery in FS2002.
Please note, not to scale and images are not oriented on the same heading.

In this article I will use PAF Shahbaz (aka Jacobabad), an Air Force base in Pakistan used by the US for operation Enduring Freedom as an illustrative example. I tend to develop a lot of projects for Pakistan because it's really a challenge getting even the most basic information. It's also a good means of testing ones ability to acquire information from different sources and compare it. For example, I undertook the task of creating a joint civil/military airport (Islamabad Airport), civilian charts (Jeppesen's) did not show the full layout of the airport (most likely due to its military nature) while the satellite photo did. Comparing this with airport data created a little fuzzy picture, but with the aid of the satellite photo the whole information could easily be refined and errors/omission corrected.

The red box indicates an area we will look at in more detail later.

Once you have obtained an image for your project there are some things to consider...

Resolution

The resolution of a satellite is very similar to that of you computer's monitor, except that it's more like a map in that 1 pixel of the image is directly proportional to a given square area on the Earth's surface.

1m resolution = 1 pixel = 1m² equivalent to 1 square meters (or 3.281 ft square)
2m resolution = 1 pixel = 2m² equivalent to 2 square meters (or 6.562ft square)
and so on...

The lower the resolution factor, the more detailed the image is, so a 0.5m resolution image shows the features more accurately than a 2m resolution image.

One other thing to remember is that satellite images are in most cases north orientated, which of course makes things a little easier on the development side. If not north oriented, then you may need need to rotate your image accordingly.

Pure Image vs Scaled Image

A pure image (one that has not been altered or re-sized) is preferred because it's more difficult to use an image that has a duff aspect ratio. The aspect ratio (or relation between width and height) is important because if it's changed then the resolution of the image will alter and the above rules about x pixels = x square area will differ. The resolution is important because it makes it easy to measure objects in the image, like a runway, building or feature.

Try to get hold of images directly from the sources mentioned below and beware of using an image from any old web site for the basis of your project as it's almost certainly been re-sized to fit their page, thus the scale will be different!

That said, if you have no option but to use such a photo, then you will have to measure a feature in the image (usually a runway works best) and need some reliable source for comparison so that you can scale the image properly in Airport Designer.

Using Airport Designer

"Airport" is a great tool to use in combination with imagery. It allows you to import a scaled background image such as an airport chart or satellite photo.

A screen shot of airport designed with the satellite image correctly loaded.

This shows the method of tracing the image using polygons and other appropriate scenery objects.

By far the simplest way to do this is is as follows...

Trim your image to show only the region your project is concerned with. Don't in any way shrink it or stretch it.
Add a runway to the project at the correct heading and dimensions.
Import the picture as a background map in Airport, typing in something like 10 as the scale to start off with.
Using some airport data, i.e. length and width of runway, carry on adjusting the scale until the runway in the project aligns with that in the photo as best as possible.

If you don't have a runway in your scenery, that's OK, but you'll have to know the size of something else in your image to use as an anchor or placeholder to work out the scale from.

Having done all of these things you are now ready to start tracing the image as the figures above show.

End Result

OK drumroll please...

Final schematic diagram of the project from Airport (area we looked at is in red).

This shows the end result of all the hard work and painstaking tracing of the underlying image.

If you have traced the image and properly done your sums correctly, then you can rest assured that your project is accurate when you fly your aircraft around it!

Tips And Tricks

The best way to get an accurate result in your scenery is to use the technique above using a feature in your image of a known size and working out the propotions of everything else.

A little math and trigonometry can also be of help.

Degrees Minutes Seconds to Decimal Lattitude Longititude calculations.
Pythagoras Theorem. (Allows you to calculate angles of triangles from area or lengths of sides vice versa), as well as the distance between two points.

On most occasions you probably won't need the above, but sometimes it comes in handy.

Sources Of Satellite Imagery

There are various establishments that provide satellite imagery. In fact, you can easily pay around £10 for a photo of a famous Landmark or city by entering your credit card details and downloading. However when it comes to airports, airfields and most especially imagery of air bases then the challenge really starts to take on form.

There is a major alliance between Aerial Imaqes and Sovinformsputnik (Russian Aeronautical and Space Agency) in the form of a web site called TerraServer.com You can browse their database driven web site and easily purchase images. However most of the world coverage images here are fairly old and are the result of ageing SPIN-2 satellite technology (ranging from 8m to 2m resolution). Those of you who are interested in US coverage will be happy to know that they host OrbImages (1m resolution pics).

In essence, this is in fact a huge de-classification of previously secret Russian satellite imagery albeit with the exclusion of some militarily important areas!

By far the biggest problem I found with TerraServer was that cities covered had their airports ommitted, by means of a big black or white polygon in place of where the airport should have been. In fact, there are reports that the US government is buying the rights to some of the Afghanistan imagery during the period of Operation Enduring Freedom, so it would be wise not to expect the availability of photos on politically or militarily hot regions.

SpaceImaging is an excellent resource. It has a wide range of products and very high quality images. There's also an image of the week feature, which ranges from a hight resolution color image of the famous mosque in Mecca as well as a recent picture of the Olympic Games. There is an archive of free images including one of Ronald Reagan Washington Airport.

SpaceImaging's commercial products are diverse and of course differ greatly in price. This is true for all commercial imagery companies, some imagery sets can be as expensive as £150,000, but it really depends on who you buy from and what you are after!

More Resources

For more information and for satellite coverage of Pakistani airports and bases, as well as flightsim and satellite comparisons, please visit the "Satellite Photos Section" of my web site.

The PAF Shahbaz (Jacobabad) scenery files can be downloaded from FlightSim.Com.

Pakistan Aviation Web site:
www.PakFlightSim.com & www.PakAviation.com

Space Imaging Web site:
www.SpaceImaging.com

TerraServer Web site:
www.TerraServer.com

Jamie Al-Nasir
Jamie@pakaviation.com

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