Keywords: motion, ppd

Summary

This demo shows how to put moving geometry in to a scene using the Generic motion model. A car is shown driving in a circle on a flat ground plate using a .ppd file to describe the position and orientation vs. time.

Details

This demo focuses on the application of the Generic motion model to describe the location and orientation of an object as a function of time. Although this motion model is commonly used for the imaging platform, the model can also be associated with scene geometry.

Important Files

This section highlights key files important to the simulation.

The plane geometry and motion

This motion of the car was created using a simple C++ program (see circle.cpp), which produced the an ASCII/Text file containing the location and Euler angle rotations (all in Scene ENU coordinates) as a function of time (see circle.txt). The program simply computes locations along the perimeter of circle with a 10 meter radius. The Z angle for each position is computed to rotate the heading of the car to be tangent to the circle. The generated ASCII/Text location and orientation file is shown below:

0 10 0 0 0 0 3.14159
0.05 9.8828 1.52649 0 0 0 3.29484
0.1 9.53396 3.01721 0 0 0 3.44809
...
[lines deleted for documentation purposes]
...
1.9 8.96166 -4.4372 0 0 0 2.68185
1.95 9.53396 -3.01721 0 0 0 2.8351
2 9.8828 -1.52649 0 0 0 2.98834

This file was then imported into a PPD file using the wizard available via Tools → Import Data in the Generic Platform Motion Editor. The resulting file was saved to geometry/sedan_red_subaru.ppd.

The geometry of the car is contained in the Alias/Wavefront OBJ file geometry/sedan_red_subaru.obj. This object is placed in the scene via the geometry/demo.glist file with a single dynamic instance:

<dynamicinstance>
  <motion type="generic">
    <options starthidden="true" endhidden="true"/>
    <filename>$SCENE_DIR/geometry/sedan_red_subaru.ppd</filename>
  </motion>
</dynamicinstance>

The <options> element is optional and can contain the starthidden and endhidden elements. When set to true these options will cause the instance to be "hidden" (invisible, no present, etc.) at times before the first time entry and/or after the last time entry.

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.

images/demo.png
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 36 separate image files for the 36 captures. The animation below was created from these 36 frames.

images/video.gif
Figure 2. The output of the simulation shows the plane rotating about it’s along-track axis during the transect.