AEM File

What are AEM files and how to open them

Are you having problems opening an AEM file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your AEM files.

What is an AEM file?

An .AEM file is a STK Azimuth-Elevation Mask Format file.

The STK Azimuth-Elevation Mask Format is an ASCII text file used by the Systems Tool Kit (STK) software to define how terrain or other obstructions block line-of-sight in terms of azimuth and elevation angles around a facility, place, sensor or target. The file allows STK to model visibility constraints by specifying the minimum elevation angles required along different horizontal directions (azimuths) to avoid obstructions such as terrain.

Such a file is written either by STK itself - automatically when the "Use terrain data" option is selected for an Az-El mask - or supplied by users to set custom angular exclusion zones for sensors, facilities, or targets. STK reads the AEM file to limit access, compute visibility, and display the mask graphically.

The file begins with a version stamp (e.g. "stk.v.6.0") followed by a block delimited by "BEGIN AzElMask" and "END AzElMask". Between these are keywords such as "NumberOfPoints", optional range‐dependent mask settings (for STK‐generated files), and "BEGIN AzElMaskData" marking the start of data lines. Data lines in basic files list pairs of azimuth and elevation angles (azimuths typically from 0° to 360°, elevation from -90° to +90°) describing the elevation thresholds for each azimuth direction. Range-dependent masks include additional columns and blocks: each azimuth line gives the azimuth degree, a maximum elevation for beyond the max range, and a count of elevation/slant range pairs where each pair gives the elevation required to avoid masking up to that slant range.

Files include a signature at the start: an ASCII version stamp beginning with "stk.v" at offset zero. They contain keywords such as "BEGIN AzElMaskData", "NumberOfPoints", and "END AzElMask" to delimit sections.

How to open AEM files

Important: Different programs may use files with the AEM file extension for different purposes, so unless you are sure which format your AEM file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested four different AEM openers which you will find listed below.

Last updated: August 17, 2026

Various apps that use files with this extension

These apps are known to open certain types of AEM files. Remember, different programs may use AEM files for different purposes, so you may need to try out a few of them to be able to open your specific file.

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