The sensor instrument must be positioned within the scene in order to capture data. In the case of a 2D framing array type of system, the instrument might be placed at a single, static location and the image acquired. For scanning systems, the instrument may rely on the motion of the instrument through the scene to acquire some spatial dimension of the instrument. In the DIRSIG model, the instrument is always placed on a "platform" that can be positioned and oriented within the scene. This chapter focuses on the use of the platform models available in DIRSIG4 to position the imaging instrument either statically or as a function of time.
The platform modeling support in DIRSIG3 was very simple. The user can use one of six different methods (three static and three dynamic) to position and orient the platform. The position and orientation of the sensor is described in the POSITION section within the PLATFORM section of the DIRSIG Input Configuration File.
In DIRSIG4, the behavior of the DIRSIG3 model is preserved in a platform model called the "classic" platform model. It is accessed by using the same POSITION section description within the PLATFORM section of the DIRSIG Input Configuration File. However, the "classic" platform model has several limitations:
The user can not specify a "twist" or rotation angle about the line-of-site when using the static positioning options.
The orientation angles are not well documented which makes it difficult for users to create location/orientation files for complex platform pointing maneuvers.
The order of the orientation rotation is fixed, and many users do not like the chosen order.
The location/orientation file specifies entries for each instrument scan/capture rather that way points that would be temporally interpolated based on the scan rate.
To learn more about the "classic" platform model, consult the Platform Modeling chapter.
In DIRSIG4, a new platform model was created that addressed most of these limitations. This "generic" platform model is well documented and the user can specify the order of the axis rotations.