DIRSIG can output auxiliary image data regarding individual steps in the image formation chain. For algorithm developers, these images can be used as ``truth data.'' This data can also be helpful in debugging the appearance of unexpected phenomenology.
The latest version of DIRSIG allows the user to control which truth images will be generated. This is controlled by the TRUTH_IMAGES section in the CFG file. If the TRUTH_IMAGES section does not appear in the CFG file, then DIRSIG will include the the default list contained in the file $DIRSIG_HOME/lib/data/misc/truth_images. To customize your installation for all the users using DIRSIG, this file can be changed to reflect the default images your facility desires. The truth images will only be generated if the ENABLE_TRUTH_IMAGES variable in the OPTIONS section is set to TRUE.
If individual user wishes to override the default truth image list, then the TRUTH_IMAGES section can appear in the CFG file. This section from our example file is shown below.
TRUTH_IMAGES {
IMAGE_FILENAME = example_truth.img
MATERIAL_MAPS = TRUE
SHADOW_MAPS = TRUE
SHAPE_FACTOR_MAP = FALSE
HIT_MAPS = TRUE
PATH_ANGLE_MAPS = TRUE
TEMPERATURE_MAPS = TRUE
EMISSIVITY_MAPS = FALSE
UPWELLED_RADIANCE_MAPS = FALSE
DOWNWELLED_RADIANCE_MAPS = FALSE
SOLAR_RADIANCE_MAPS = FALSE
PATH_TRANSMISSION_MAPS = FALSE
PLUME_MAPS = FALSE
}
Any of the images set to true TRUE are generated. A description of each truth image or images is discussed in the following section. The truth images take the form of a single multi-band image file that contains a single band for each truth image generated. An ENVI compatible header file is also generated that includes the name of the truth image assigned to each band so that the user can easily browse the truth data in either ENVI or Freelook.
Each of the truth map images indicates the specified value on a pixel-by-pixel basis. In some cases, the truth image will be generated for each bandpass the user has specified in the BAND_LIST section.
The truth images are written to a file named truth.img by default. IF the user wishes to change the name of this file, the IMAGE_FILENAME variable can be set to the desired filename.
DIRSIG will generate a series of material or classmap images. The images contain the Material IDs of the various types of facets (opaque or transmissive) intersected at each pixel.
Material ID of the first facet
Material ID of the first opaque facet
Material ID of the first transmissive facet
DIRSIG will generate a series of shadow masks. Each of the images in this series will contain the values 0 to indicate shadow, or 1 to indicate no-shadow for the source or sources of interest.
Solar shadow mask
Lunar shadow mask
Man-made sources shadow mask
The shape factor or sky exposure image contains values between 0.0 and 1.0 to indicate the fraction of sky that the hit point was exposed to. A value of 1.0 indicates 100% sky exposure. These values will be 1.0 unless the ENABLE_BRDF variable in the OPTIONS section is set to (see Section 32.5).
The hit map series contains the X, Y, and Z location of each pixel in scene units. These images can be valuable for identifying why a specific object was not imaged or in setting up new viewing geometries.
X location of hit point [scene units]
Y location of hit point [scene units]
Z location of hit point [scene units]
Facet normal to sensor view angle [degrees]
The path angle images indicate the zenith (from vertical) and azimuth (East-of-North) angles of the path to each pixel in the output images.
The truth data is measured from the scene's global normal (0,0,1). For example, a truth zenith of 135 degrees and a truth azimuth of 270 degrees indicates that the ray traced from the sensor is traveling at a 45 degree downwards slant towards due west. Note that from the global ground plane perspective, this same ray is approaching from 45 degrees above the horizon coming from the east.
Zenith angle of primary path [degrees]
Azimuth angle of primary path [degrees]
The temperature map series indicates the predicted temperature of the opaque and transmissive facets intersected at each pixel in the image. Surface temperatures are only computed if the ENABLE_THERMAL_MODEL variable in the OPTIONS section is set to (see Section 32.5).
Temperature of the first facet
Temperature of the first opaque facet
Temperature of the first transmissive facet
The emissivity map series indicates the average emissivity for each sensor band of the intersected facet at each pixel in the image. If the user configures N different spectral bands, N emissivity maps will be generated.
The upwelled radiance map series indicates the integrated upwelled radiance for each sensor band in the image. If the user configures N different spectral bands, N upwelled radiance maps will be generated.
The downwelled radiance map series indicates the integrated downwelled radiance for each sensor band in the image. If the user configures N different spectral bands, N downwelled radiance maps will be generated.
The solar radiance map series indicates the integrated solar radiance reaching the intersected facet for each sensor band in the image. If the user configures N different spectral bands, N upwelled radiance maps will be generated.
The path transmission map series indicates the average path transmission from the sensor to the intersected facet for each sensor band in the image. If the user configures N different spectral bands, N upwelled radiance maps will be generated.
The plume image series contains images including the integrated emission (radiance) from the plume, the bandpass average transmission through the plume, the average plume temperature, and the column density of each gas in the plume.
Integrated plume radiance
Average plume transmission
Plume temperature [C]
Gas Column Density [ppm-m] (one image for each gas)