Keywords: BRDF

Summary

This scene provides a way to compare the reflections of background targets by two materials that have the same reflectance configuration except with a difference in surface roughness.

Related Materials

The following demos, manuals and tutorials can provide additional information about the topics at the focus of this demo:

Details

This demo shows how the surface roughness parameter in the parametric Priest-Germer BRDF model impacts the reflectances of the background.

Important Files

This section highlights key files important to the simulation.

Scene

The scene is composed of a set of panels:

  1. The wide-area, background (grass) panel (see Background.gdb),

  2. The two large, flat "mirror-like" panels at the focus of this demo (see PolishedPanel.gdb and DullPanel.gdb), and

  3. Two pairs of Black/White panels (see BlackPanel.gdb and WhitePanel.gdb) that are reflected by their respective "mirror-like" panels.

The scene layout defined in the geometry/demo.odb file.
DIRSIG_ODB = 1.0

OBJECT {
    GDB_FILENAME = Background.gdb
    UNITS = METERS
    INSTANCES {
	    INFO = 0.0, 0.0, 0.0, 100.0, 100.0, 100.0, 0.0, 0.0, 0.0
    }
}

OBJECT {
    GDB_FILENAME = PolishedPanel.gdb
    UNITS = METERS
    INSTANCES {
	    INFO = -10.0, 11.0, 0.01, 20.0, 20.0, 20.0, 0.0, 0.0, 0.0
    }
}

OBJECT {
    GDB_FILENAME = DullPanel.gdb
    UNITS = METERS
    INSTANCES {
	    INFO = -10.0, -11.0, 0.01, 20.0, 20.0, 20.0, 0.0, 0.0, 0.0
    }
}

OBJECT {
    GDB_FILENAME = WhitePanel.gdb
    UNITS = METERS
    INSTANCES {
	    INFO = 0.0, -13.5, 5.0, 10.0, 5.0, 1.0, 0.0, -90.0, 0.0
	    INFO = 0.0, +8.5, 5.0, 10.0, 5.0, 1.0, 0.0, -90.0, 0.0
    }
}

OBJECT {
    GDB_FILENAME = BlackPanel.gdb
    UNITS = METERS
    INSTANCES {
	    INFO = 0.0, -8.5, 5.0, 10.0, 5.0, 1.0, 0.0, -90.0, 0.0
	    INFO = 0.0, +13.5, 5.0, 10.0, 5.0, 1.0, 0.0, -90.0, 0.0
    }
}

Materials

The materials/demo.mat material file defines all the materials in this simulation. The large square panels reflecting the black and gray vertical panels are the focus of this demo. These panels are assigned the Priest-Germer BRDF model. The original implementation of this BRDF model in DIRSIG4 included the polarization component. In DIRSIG5, polarization is not modeled but Priest-Germer model as a handy surrogate for the simple Torrance-Sparrow model. Both of these BRDF models require the user to provide the complex index of refraction (i,j) and surface roughness as a function of wavelength. The DIRSIG input files for the "dull" and "polished" surface materials are shown below:

The Priest-Germer BRDF for the "dull" surface.
0.53904 0.250 0.8260 6.2830
0.56354 0.250 1.0180 6.8460
0.61990 0.250 1.3040 7.4790
0.66678 0.250 1.7410 8.2050
0.77487 0.250 2.6250 8.5970
The Priest-Germer BRDF for the "polished" surface.
0.53904 0.050 0.826 6.283
0.56354 0.050 1.018 6.846
0.61990 0.050 1.304 7.479
0.66677 0.050 1.741 8.205
0.77487 0.050 2.625 8.597

As you can see, the old difference is the surface roughness (2nd column) in the input.

Simulations and Results

Run the demo.jsim file using DIRSIG5:

$ dirsig5 demo.jsim

The output radiance image can be scaled to a PNG using the DIRSIG image_tool utility:

$ image_tool convert --autoscale=gamma demo.img
The output image using the default gamma scaling.

demo