System Requirements

Operating Systems

The DIRSIG software is distributed for the following platforms:

  • The Windows platform

    • OS: Windows 8 and Windows 10

    • Processor: Intel/AMD x86 64-bit

    • Format: Windows MSI installer (.msi)

  • The Linux platform

    • OS: Any 2.6 or later kernel

    • Processor: Intel/AMD x86 64-bit

    • Format: tar+gzip archive (.tgz)

  • The MacOS platform

    • OS: 10.14 (Mojave), 10.15 (Catalina), 11.x (Big Sur) and 12.x (Monterey)

      • Installation currently requires Gatekeeper to allow applications to run that were downloaded from "Anywhere"

    • Processor: Intel x86 64-bit and Apple Silicon 64-bit (ARM64)

    • Format: Disk image (.dmg) containing the software as a folder to be copied into the system Applications folder or user folder.

Hardware Requirements

The following hardware recommendations:

  • A recent Intel/AMD CPU with clock rates of 2 GHz or higher.

  • At least 2 GB of memory (RAM).

  • At least 2 GB of disk space.

    • The user should expect to use significantly more disk space when they begin to generate data with the model.

  • There is no minimum requirement for video cards and displays.

    • Any display hardware that would be present in the previously outlined machine tends to be sufficient.

Software Requirements

The following software is required:


    • A copy of MODTRAN4, MODTRAN5 or MODTRAN6 is required for rigorous atmospheric modeling

      • MODTRAN4 Version 3 Release 1 or later

      • MODTRAN5 2.0.0 or later

      • MODTRAN6 6.0.0 or later

    • Read the MODTRAN guide for more information on how to setup DIRSIG to use your copy of MODTRAN.

    • Visit for more information on how to obtain a copy of MODTRAN5

The DIRSIG software comes with a built-in image viewer, however the following software is recommended for additional image viewing, manipulation and/or processing.

  • A copy of an image exploitation tool such as ENVI or Opticks can provide advanced image/data viewing and analysis of the image files produced by DIRSIG.

  • A copy of a LIDAR exploitation tool such as MARS FreeView or QuickTerrain Reader can provide advanced viewing and analysis of LAS format 3D point clouds produced by DIRSIG.

Execution Requirements

The following clarifications might be useful to system administrators:

  • DIRSIG does not need "administrator" privileges to run. The end user simply needs:

    • Execute permissions for the programs, and

    • Read-only access to the support files included in the installation.

  • DIRSIG does not have any "phone home" mechanisms (for example, to check for software updates)

    • The default option is to use the HTML documentation installed with the software. However the end-user can change that to access the HTML documentation source on the DIRSIG website.


A standard DIRSIG release contains the following:

  • A set of executable programs

  • A collection of HTML-formatted support documents

  • A set of demonstration (example) simulations

  • A folder of "extras" that include Matlab and Blender scripts for various tasks.

General File and Folder Layout

A DIRSIG release includes a copy of the latest DIRSIG4 (maintenance updates only) and DIRSIG5 (active development).

The bin folder

This folder contains a full set of the DIRSIG programs.

The demos folder

This folder contains the standard DIRSIG demos.

The docs folder

This folder contains all of the DIRSIG documentation, including release notes and this document.

The extra folder

This folder contains various "extras" including the Blender plugins, BIN file reader for Matlab and MODTRAN6 wrapper that can be used with Linux and MacOS to resolve shared library location issues.

The lib folder

This folder (not present on Windows) contains the dynamic (shared) libraries that are used by the executables. On Windows, all dynamic libraries (DLLs) are in the bin folder.

The plugins folder

This folder contains all the DIRSIG5 plugins that provide most of the functional utility to the radiometry core. This currently includes sensor models and atmospheric plugins.


The DIRSIG software is released on the Windows platform as a traditional Windows installer (with a .msi extension). Simply double-click the installer file and follow the standard directions to install the software. The DIRSIG installer is signed with RIT’s "Code Signing Certificate" to indicate that it was indeed produced by RIT. However, Windows Defender SmartScreen may still flag the installer as "unrecognized" because RIT does not also have a "Extended Validation (EV) Code Signing Certificate".

signed windows installer1
Figure 1. Windows Defender SmartScreen "unrecognized" application warning.

Hence, the user might be required to tell Windows Defender that the application is recognized by clicking on the More Info hyper-link, verifying the installer and publisher and then clicking the Run Anyway button:

signed windows installer2
Figure 2. After clicking the "More Info" hyper-link, tell Windows Defender to "Run Anyway".

Finally, a Windows User Access Control (UAC) dialog should appear that confirms you want to proceed with the installation:

signed windows installer3
Figure 3. The UAC dialog should indicate you are installing DIRSIG published by Rochester Institute of Technology.

The default install location for DIRSIG is the C:\Program Files\DIRSIG folder.


The DIRSIG software for the LINUX platform is released as a tar+gzip archive that contains the program executables, supplemental data, basic scenes, etc. The installation of the software is as simple as choosing a location, unpacking the archive into that location, and setting up your user environment.

There are no requirements or assumptions about where the DIRSIG installation will be located. An administrator with the correct permissions can install DIRSIG in a common area (for example, /usr/local or /opt) so that multiple users can access the single installation. A single user without special permissions can install DIRSIG in a directory in their account.

For the remainder of this explanation, we will assume that the DIRSIG software will be installed in /opt/rit/dirsig (which will most likely require superuser permissions) and that the DIRSIG installation archive file is located in the /tmp (the user can obviously adapt these instructions to deal with the installation destination or source archive file being in any location).

Note The choice of /opt/rit/dirsig as the installation folder is just an example. Any accessible folder is valid.

To create the installation directory, execute the following command:

$ mkdir /opt/rit/dirsig

Then, make sure you are at the top of your installation directory:

$ cd /opt/rit/dirsig

Then unpack the DIRSIG installation archive. On the LINUX platform this can be done using the tar command (which has gzip compression support built-in):

$ tar -xzvf /tmp/dirsig-2021.42.0.8021a56.tar.gz


The DIRSIG software is released on the MacOS platform as a single application bundle. The software is installed like many MacOS software packages:

  • Mount the disk image by double-clicking on the .dmg file.

  • Open the mounted disk image in Finder (it should have appeared as a new volume after you mounted it).

  • Drag the application bundle into the system Applications folder (which will require admin privileges), the user’s Applications folder, or any accessible folder.

  • Double-click on the application bundle to start the graphical user interface (GUI).

  • If you plan on using DIRSIG via the command-line, then you will need to modify your login files to include [InstallFolder]/ folder in your path (where [InstallFolder] reflects the location of the DIRSIG app, e.g., /Applications, etc.).

Note As of the 2022.47 release, the DIRSIG application bundle (aka has been signed and notarized by Apple and should not need any additional permissions or executable exceptions or overrides to run.

Optional DIRSIG5 Site Configuration

There is an optional installation configuration file that allows the installation administrator to control some key parameters for all users. These parameters generally control how compute resources are utilized by individual users.

The INI formatted configuration file is called dirsig.ini and needs to be placed in the top of the installation folder (at the same level that the bin, plugins, etc. folders are located). If the file does not exist or a given parameter is not present, a set of default values are used. An example file is shown below:


Defines the maximum number of threads that can be started by an individual simulation. The default value is the number of virtual cores present.


Defines the default number of threads started by an individual simulation. The default value is the maximum number of threads. This number can be overridden for a simulation by the --threads command-line option. If the number of requested threads exceeds the maximum, an error is issued.

The idea behind the maximum and default thread count parameters is to help the installation administrator manage a compute resource being shared by many users and/or services. For example, you might have a machine with 32 cores and many users. Without setting the maximum thread parameter, a single user could start up a simulation that spawns a massive number of threads, leaving very few resources for other users. The maximum value is to define the maximum number of threads a single user could ever launch from a single simulation.

Note This parameter does not span processes or replace operating system level resource management. A single user could still launch multiple simulations that use additional thread pools.

The default thread count is the number of threads used by any simulation. This value can be less than the maximum if you want to create an environment where users can request more threads if needed (via the --threads command-line option), but by default they use a modest amount.


This section outlines the process to upgrade an existing DIRSIG installation to a newer release.

Important If you are upgrading from DIRSIG 4.4 or earlier, it is strongly recommended that you uninstall DIRSIG prior to installing DIRSIG 4.5 or later.
Important If you are upgrading from DIRSIG 4.4 or earlier, MacOS users should delete the DIRSIG_HOME key/string pair from your ~/.MacOSX/environment.plist file (which is no longer required). This task can be performed with a .plist file capable editor such as TextWrangler or Xcode.
Tip The default behavior of most installers is to replace a previous installation with the new version. If you want to keep a copy of the previous version when you install a new version, the best approach is to make a copy of the installation prior to installing the new version.


The .msi installer can be run directly as outlined in the Installation section above. Installing an update will replace the previous version of DIRSIG.


The recommended option for upgrades is to create a whole new installation directory for each installation. In this approach, rather than installing to /opt/rit/dirsig, the user might unpack into /opt/rit/dirsig-2021.42.0.8021a56. When the 2021.xx release arrives, the user can unpack that release into /opt/rit/dirsig-2021.xx.0.yyyyyy. To simplify this scheme for users, you might consider making a symbolic link called /opt/rit/dirsig that always points to the current installation directory. Again, the installing user will want to purge old installation folders over time.


To keep an previous version of the software, the process is straightforward. Since the installation is a simple drag and drop process, the user can rename an older installation folder (for example, DIRSIGDIRSIG-2021.42) prior to copying the new version.

Using the Software

First time users will be greeted with the DIRSIG User Setup Wizard the first time they start the graphical user interface. This wizard will guide them through the process of setting up their personal settings, including telling DIRSIG where MODTRAN is installed. More information about setting up DIRSIG to use MODTRAN is discussed below.


Starting in DIRSIG 4.5, information required by DIRSIG to locate and run MODTRAN is stored in each user’s personal settings. This new method allows each user to configure multiple MODTRAN installations, and then select which MODTRAN installation is used during a given simulation.

Note A given user’s list of MODTRAN installation profiles might include stable versus experimental versions of MODTRAN.

First time DIRSIG users will be prompted by the DIRSIG User Setup Wizard to configure a MODTRAN installation profile. In addition, users can always add, remove or modify a MODTRAN installation profile via MODTRAN tab in the Preferences window for the user interface.

Each installation profile requires three pieces of information:

  • The path to the MODTRAN executable file

  • The path to the MODTRAN DATA folder

  • The minimum spectral delta supported by that version

    • This is 1 wavenumber (1/cm) for MODTRAN4 and 0.1 wavenumber (1/cm) for MODTRAN5

Important The standard Windows distribution of MODTRAN5 can contain two executables: one ending with qwin.exe and one ending with cons.exe. You must select the _cons.exe version (which is a "console only" application suitable for being called by other programs) for use with DIRSIG.
Important The standard MacOS distribution of MODTRAN5 has dependencies on dynamic libraries that are included with the distribution. However, to run MODTRAN5 from outside the installation folder (which is required by DIRSIG), then you should consult this note.

If you are having problems with DIRSIG integrating with MODTRAN, consult the MODTRAN Integration Guide and the Troubleshooting Guide.

Command-Line Usage

DIRSIG is distributed with a graphical user interface (GUI) that allows the user to configure and run a DIRSIG simulation without using any command-line tools. However, there are still many reasons you might want to run a DIRSIG simulation from the command-line. To learn more about the command-line aspects of the model, consult the DIRSIG5 Command-Line Guide.


The Windows installer should have automatically added the folder containing the DIRSIG executables to the path used in the CMD and PowerShell environments.

Linux and MacOS

If you want to run DIRSIG from the command line then your login shell will need to have the path to the DIRSIG executables configured. The default shell for many accounts on Linux is bash, but many users use csh or tcsh. The automatic setup of environment variables in your login shell is slightly different for each shell, but the general requirements for each are the same. If you are a novice at setting up your shell environment, consult the documentation for the shell you are using or ask an experienced user or administrator.