Keywords:

Summary

This demo shows how a component (aka "part" or "group") within a facet object can be assigned motion. In this case, the missle on a simple mobile missle launcher is commanded to transition from an erect position to a lowered position. Additionally, this demo shows how the sub-object properties feature in the GLIST can be used to override a material based on the part (group) the facets belong to.

Related Materials

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

  • Related Demos

  • Related Manuals

    • The GLIST manual, specifically this section on defining sub-object properties.

  • Related Tutorials

    • N/A

Details

The key aspect of this demo is associating motion with a component of a single object without the need to break the object into multiple objects to associate the motion through the traditional instance assigned motion mechanism. Motion can be associated with any "part" of the object as long as it is a "group" entity in the input OBJ filename.

In addition to showing how to associate motion with a part, this demo shows how to change the materials assigned to a part and how a part can be disabled.

Important Files

All of the important details are contained in the GLIST file that imports the SS1 vehicle (see geometry/demo.glist) and positions it within the scene. The relevant <object> section is included below:

  <object tags="ss1">
    <basegeometry>
      <obj>
        <filename>ss1.obj</filename>
        <properties>
          <part name="CRADLE" enabled="true">
            <origin><x>0</x><y>-5.75</y><z>2.0</z></origin>
            <motion type="delta">
              <movement>$SCENE_DIR/geometry/lower.mov</movement>
            </motion>
          </part>
          <part name="MISSLE" enabled="true">
            <matid>missile</matid>
            <origin><x>0</x><y>-5.75</y><z>2.0</z></origin>
            <motion type="delta">
              <movement>$SCENE_DIR/geometry/lower.mov</movement>
            </motion>
          </part>
        </properties>
      </obj>
    </basegeometry>
    <staticinstance>
      <translation>
        <point><x>1</x><y>-3</y><z>0</z></point>
      </translation>
      <rotation rotationorder="xyz" units="degrees">
        <cartesiantriple><x>0</x><y>0</y><z>240</z></cartesiantriple>
      </rotation>
    </staticinstance>
  </object>

The important part of the configuration is the optional <properties> description. In this example, we name two "parts" to be modified in the original ss1.obj file. The part names correspond to groups in the OBJ file (groups are started and named using lines that begin with g, for example g CRADLE). The modifications to these parts are described below:

  • The CRADLE part is the structure that holds the missle body. In the real world, this is what holds the missle and lifts it up.

    • The <origin> for this part has been explicitly defined so the motion knows about what location to perform rotations. This location is at the base of the cradle where it pivots, near the rear of the vehicle (hence, the negative Y value).

    • The <motion> for this part is defined by the DeltaMotion model via the lower.mov file.

  • The MISSLE part is the rocket body itself (laying in the cradle). It uses the same <origin> and <motion> descriptions because we want it to rotate about the same point and at the rate.

    • The <matid>missile</matid> changes the material the missle to ID/Label missile, which is a brighter gray.

Note
 The enabled attribute for any <part> can be set to false to disable a given part (make it disappear).

The lower.mov file is shown below and it contains a single MOVE entry which makes the X axis rotation -0.6 radians after 1 second:

DIRSIG_MOV = 1.0

INIT_POSITION {
    TRANSLATION = 0.0, 0.0, 0.0
    SCALE       = 1.0, 1.0, 1.0
    ROTATION    = 0.0, 0.0, 0.0
}

MOVES {
    # dSeconds dTX dTY dTZ dSX dSY dSZ dRX dRY dRZ
    MOVE = 1.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.6, 0.0, 0.0
}

The front of the vehicle is pointed down the +Y axis. The missile actually starts in an erected position, so the motion we want to lower it is a -X rotation (all DIRSIG rotations are right handed).

Setup

Single-Frame (Still) Simulation

To run the single-frame 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.

Multi-Frame (video) Simulation

To run the multi-frame 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 (Still) Simulation

The single-frame simulation produces a single image frame. Note that the missle body is the lighter shade of gray (like the background) due to the material reassignment in the <part> properties.

demo
Figure 1. Output of the single-frame simulation.

Multi-Frame (video) Simulation

The imaging instrument is setup to use the "file per capture" output schedule. As a result, the simulation produces 20 separate image files for the 20 captures. The animation below was created from these 20 frames.

video
Figure 2. The output of the multi-frame simulation.