Keywords: brdf, sqt

Summary

This demo uses a DIRSIG spherical quad-tree (SQT) to describe a measured blue paint bi-directional reflectance distributon function (BRDF) that is attributed to a unmanned airbone vehicle (UAV).

Details

This scenario focuses on the data-driven BRDF model at the core of DIRSIG5, but which was back-ported to DIRSIG4 for comparisons and DIRSIG4 utility. It stores the BRDF using a spherical quad-tree (SQT) data structure, which has some unique and powerful features including adaptive resolution (level of detail), efficient storage, efficient hemispherical integration and efficient sampling mechanisms.

Important Files

This section highlights key files important to the simulation.

The Blue Paint BRDF

The blue paint used on the vehicle in the scene was imported from the Cornell University Program of Computer Graphics (PCG) database. A description and the original measurements for this paint can be found here. The measurements were converted into a file that could be ingested by the DIRSIG5 raw2sqt tool. The input "raw" file and produced SQT file are in the matrials folders (see materials/blue_paint.raw and materials/blue_paint.sqt, respectively).

The Material Database

The BRDF for the blue paint is supplied to DIRSIG using the SphericalBRDF optical property and SQT input in the materials/demo.mat:

MATERIAL_ENTRY {
    ID = test_mat
    NAME = Blue paint
    EDITOR_COLOR = 0.5, 0.5, 0.5
    DOUBLE_SIDED = TRUE

    SURFACE_PROPERTIES {
        REFLECTANCE_PROP_NAME = SphericalDataBRDF
        REFLECTANCE_PROP {
            DATA_FILENAME = blue_paint.sqt
        }
    }

    RAD_SOLVER_NAME = Generic
    RAD_SOLVER {
        INITIAL_SAMPLE_COUNT = 100
        SAMPLE_DECAY_RATE    = 5
        MAX_BOUNCES          = 2
        MU_SAMPLES           = 8
        PHI_SAMPLES          = 12
        MIN_QUAD_SAMPLES     = 1
    }
}

Setup

There are two simulation scenarios in this demo:

  1. A single-frame simulation

  2. A multi-frame (video) simulation

Running the Single-Frame Simulation

This single-frame simulation produces a single image file. To run the simulation, perform the following steps:

  1. Run the DIRSIG demo.sim file

  2. Load the resulting demo-t0000-c0000.img file in the image viewer.

Running the Multi-Frame Simulation

The multi-frame simulation produces 41 image files. To run the simulation, perform the following steps:

  1. Run the DIRSIG video.sim file

  2. Load the resulting demo-t0000-c0000.img, demo-t0000-c0001.img, etc. files in the image viewer.

Results

Single-Frame Simulation

The single-frame simulation produces the single-frame simulation shown below:

images/demo.png
Figure 1. Output of the single-frame simulation (two percent scaling).

Multi-Frame Simulation

The output of the multi-frame simulation is a series individual image files. The frames can be scaled and encoded into a video format for viewing using a variety of 3rd party software tools (ffmpeg, mpeg_encode, etc.).

images/video.gif
Figure 2. Animation of the multi-frame "video" collection.