DIRSIG

Like most ray tracing environments, DIRSIG offers a number of convenient primitive objects to use in place of facetized geometry. Aside from offering a quick way to construct a (simple) scene, primitives have mathematically defined surfaces so there is no reason to worry about edges between facets. In contrast to vertex normal interpolation which helps smooth the appearance of facetized objects, primitives offer true, smooth geometry which can be convenient for working out precise radiometry problems. We've already made some of these primitive objects available under the old object database (ODB) inputs, which has been shown in the PrimitiveObjects1 demo. These objects are shown below. The primitives shown are a box, a sphere, a cylinder, a ground plane, a disk, and a two material disk (introduced to quickly model a Secchi disk for virtually measuring turbidity). We've now updated the "glist" format to support these primitives and to provide previously unavail...

As many of you may have read in past posts by Niek , we have been using the Blender software heavily in the construction of scenes so they can be ingested into DIRSIG . While we have many Blender tools that work in the editing and exporting of existing scenes, they only utilize a small subset of features that exist in Blender. Blender can be viewed as the vi (or emacs) of the 3D animation world which means it can be very powerful but at times opaque to the newly initiated. After paying our dues in the apprenticeship of Blender knowledgedom, we wanted to make accessible to DIRSIG users the capabilities that have made Blender the de facto standard of the 3D animation domain. In an ongoing project that addresses the need of data sets for training machine learning algorithms and assessing the performance of target detection/exploitation algorithms, DIRS has focused on implementing tools for producing numerous instantiation of simulated scenes. Blender has been an integral part ...

A new "refinery" scene will be included in the next DIRSIG release. The scene was inspired by the Ras Lanuf oil refinery in Libya.  It features an industrial site sitting on a desert-water interface.  Two DIRSIG renderings are shown below. The highlight is the refinery itself, featuring pipes and general industrial clutter.  The plant connects to a railroad track and an access road.  A small oil carrying ship is anchored nearby.  The desert itself is filled with shrubs. As with the Warehouse scene, the geometry was placed using our Blender scripts .  This refinery scene took roughly a week to construct.

In a previous post, we discussed the advantages of using OBJ files in DIRSIG. This tutorial video shows how Blender can assign DIRSIG materials to an OBJ geometry mesh.  Basic familiarity with Blender is a prerequisite. Attributing an OBJ with DIRSIG materials (video) The idea is simple: in the OBJ file, the "use material" ( usemtl ) string will specify a DIRSIG material id rather than just an arbitrary material name.  The OBJ's "material library" ( mtllib ) string is ignored by DIRSIG.

For quite some time, the DIRS lab has been using Blender to build small DIRSIG scenes. Blender is an advanced, open source, cross-platform, 3-D modeling package. It is available free of charge, but it has a fairly steep learning curve. We've created Blender plug-ins allowing us import and export some of DIRSIG's native formats, including GDB and ODB. Blender also allows us to use geometry with the OBJ format . We can now create new scenes from scratch by assembling geometry, placing instances using Blender, and then saving out a DIRSIG ODB file. Traditionally, we have distributed the Bulldozer application for both attributing materials to geometry and constructing scenes. This set of plug-ins allows Blender to be used as an alternative to Bulldozer for constructing scenes. Starting with the official DIRSIG 4.4.1 release, we will be distributing these Blender scripts to the DIRSIG user community. All future DIRSIG distributions will include these scripts in the dir...

We've just put together another DIRSIG "demo" simulation. It shows a camera placed indoors. The scene is illuminated by both a secondary source at the ceiling and through a window cut-out at the far end of the room. This demonstration will be included in the next DIRSIG release.

We have placed an update to the MegaScene1 distribution on myDIRSIG. The major aspect of this release is that it comes with a set of DIRSIG4 .scene files. This release also includes updates to material properties including the conversion of the tree leaf optical properties from extinction to transmission. We have found that changing this optical property provided speed ups because a large number of calls to the exponent function (to compute the transmission from the extinction) are eliminated. You can also download an update to MicroScene1. Like MegaScene1, we had neglected to push out an update of MicroScene1 with DIRSIG4 .scene files that were as simple to use as "unzip and use". Both updated scene files can be downloaded by registered users from the myDIRSIG website.

When we first started on the DIRSIG model in the late 1980s, 3D computer graphics was still in its infancy. At the time, standard file formats for 3D geometry were still being established. In addition, the DIRSIG model had the need for a specific set of per-facet attributes (material ID, thickness, override temperature, etc.) that are still somewhat unique in the 3D modeling community. As a result, the DIRSIG specific Geometric Database (GDB) format was created and is still used to this day. In the mean time, a variety of 3D geometry file formats have become widely used. Although the GDB format serves our needs well, it requires the user to translate the 3D geometry assets from other formats in order to use them with DIRSIG. Lately we have been experimenting with using the Alias/Wavefront OBJ file format as a possible replacement for GDB. The important features of the OBJ format are: It is widely supported by 3D geometry authoring tools (Rhino, SketchUp, Blender, etc.). It supports per...

In the DIRSIG 4.4.0 release users will find that we made some modest improvements to the classic Urban and Forest scenes. Primarily, we improved the scene geometry by replacing the decade old, low facet count trees with the high fidelity trees we have been using in other scenes. We have also cleaned out a bunch of unused files and tried to improve the organization of the respective scene directories. The first thing you will notice in the updated Urban scene (seen above) is the new trees and the fact that there is more than one tree species. The scene also has some new textures for the grass and asphalt areas. This scene now has both day/night and summer/winter configurations. The "night" .scene files have the streetlights automatically enabled. The "winter" .scene files use defoliated trees. You might ask why the river running down the middle of the scene is so green in color. The river is modeled as a flat surface with an effective reflectance measured from s...

Included in the DIRSIG-4.4.0 release candidate is a new "warehouse" scene. As shown below, this scene features a fairly high amount of geometric clutter. The scene includes stacks of wood palettes and crates, steel I-beams, piles of corrugated steel panels, steel pipes, shipping containers, concrete barriers and other "cultural clutter" objects that might be found at a site like this. The scene was created with roughly a 0.10 [m] GSD in mind. It includes full spectral coverage in the visible, NIR, and SWIR. This will be extended to the MWIR and LWIR in the future. Placement of geometry and material attribution was done using Blender together with some DIRSIG I/O python scripts. The material database was manipulated using the "mat_edit" tool. The material map over the terrain was originally drawn as a vector layer using Inkscape and then cleaned and converted to its final PGM version using Gimp . In addition to adding LWIR coverage, we would like to i...