ACMI 2.2 File Format 101

Without further ado, let's start with the simplest file possible:

FileType=text/acmi/tacview
FileVersion=2.2

These are the only two mandatory lines you must put first in any ACMI file. This header tells Tacview which format to expect. Any following data is optional.

Let's be rational: Even if Tacview will gracefully load this empty file, we need a bit more data to make it useful! Here is a file which makes more sense:

FileType=text/acmi/tacview
FileVersion=2.2
0,ReferenceTime=2011-06-02T05:00:00Z
#47.13
3000102,T=41.6251307|41.5910417|2000.14,Name=C172

To better understand this structure, we need to know that – apart from its header – each line of the file can be either:

• The sharp sign # introducing a new time frame in seconds relative to ReferenceTime
• An object id (in this example 0 and 3000102) followed by as many properties as you want separated by commas ,. Each property will be assigned a new value using the equal sign =.
• A line which starts with the minus sign - followed by the id of an object we want to remove from the battlefield (destroyed or out of recording range).

Let's see in detail each line syntax:

0,ReferenceTime=2011-06-02T05:00:00Z

This line assigns the value 2011-06-02T05:00:00Z to the property ReferenceTime of the global object always designated by its id zero 0. This line defines the base/reference time used for the whole flight recording. To understand better what this means, let's have a look at the following line:

#47.13

This line defines a time-frame in seconds relative to ReferenceTime. This means that the following events or properties happened at ReferenceTime + 47.13 seconds → 2011-06-02T05:00:00Z + 47.13 → 2011-06-02T05:00:47.13Z.

Now let's see the following line:

3000102,T=41.6251307|41.5910417|2000.14,Name=C172

This line defines two properties for the object 3000102. To save space, Object ids are expressed in hexadecimal without any prefix or leading zeros.

The first property T (which stands for Transform) is a special property used to define the object coordinates in space. For now, let's just focus on the syntax: T = Longitude | Latitude | Altitude.

Notice that Latitude and Longitude are expressed in degrees. Positive values are toward the north and east directions. Since the whole file is always in the metric system, the altitude is expressed in meters MSL (above sea level, also known as ASL).

The following property Name defines the object name C172, which is a short way of designating a Cessna 172 aircraft.

Now that you know all the basics to create a flight recording, let's move our new aircraft a bit further to the east. To do so, we can simply add another frame to our file:

#49
3000102,T=41.626||

As you can see, we have defined a new longitude value 41.626 for our aircraft at the time frame 2011-06-02T05:00:49Z.

You may have noticed that we don't need to specify the aircraft name again, simply because it has not changed since the last time! Also, we omitted the latitude and altitude parameters because they did not change either. This helps to save a lot of space during long flight recordings. This optimization is especially relevant for ground objects which may remain still or move only slightly.