Keywords: jitter, motion
Summary
This demo focuses on the temporally correlated jitter tools available in the DIRSIG model. Specifically, the ability to supply a jitter frequency spectrum to any of the three dimensions of the platform location and/or orientation.
Details
A jitter spectrum is represented as a series of magnitude and phase pairs at a discrete set of frequencies. The supplied spectrum is not interpolated during run-time, but rather interpreted as a set of impulse responses that are directly synthesized.
The jitter in this scenario is associated with the X, Y and Z location of the platform. Because the same frequency spectrum (the same magnitude and phase) was used for all three dimensions, the oscillations of the platform location will be correlated.
The DIRSIG platform model supports jitter for all six degrees of freedom (the XYZ location and XYZ orientation) for the platform and each mount supports jitter in three degrees of freedom (the XYZ orientation).
Important Files
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The file
spectrum.txtcontains the ASCII/Text frequency spectrum used to drive location jitter in the platform location. This file contains three columns for the frequency, magnitude and phase. -
The generic platform motion file (
jitter.ppd) features the imported jitter spectrum (spectrum.txt), which was assigned to the X, Y and Z dimensions of the platform location.
Setup
This simulation consists of a 2D framing camera mounted to a platform that is statically positioned (a single location and orientation entry) over the scene. The jitter causes the platform and hence the attached 2D framing camera to move between each capture.
The key component in this simulation is the jitter.ppd file. The
jitter for the X, Y and Z location was setup using the following steps:
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Open the Platform Motion Editor
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Click on the Jitter tab
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Change the jitter model for the X Axis in the Location from None to Temporally Correlated.
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Click the Edit button
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In the Frequency, Magnitude and Phase table on the left side of the window (which starts empty), right-mouse click and select Import from the pop-up menu to start standard ASCII/Text import wizard.
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Select the
spectrum.txtfile included in this demo and progress through the wizard so that the 3-column file is loaded into the Frequency, Magnitude and Phase. -
This process was repeated for the Y Axis and Z Axis of the Location.
The user can also manually add entries to the frequency spectrum one at a time using the Add Entry button. Unwanted entries can be removed with the Delete Entries button.
Results
The simulation produces 30 image frames that spans the 1 second task window. Because of the platform jitter, each frame is offset from the previous and the target scene appears to dance around.
