4.2 The Reordering Utility

The mathematical and computational foundations of the least-squares bundle adjustment employed by GIANT have been thoroughly studied over the past 30 years. While the original motivation for this research was largely the limitation in early generation computer resources and equipment, savings in computer time, memory and storage continue to be beneficial and enable the completion of triangulation tasks of ever-increasing size and complexity.

One significant breakthrough in the research of efficient triangulation processing was the principle of parameter reordering. Stated briefly, when properly arranged, the triangulation of photogrammetric strips and blocks lead to equations that have specific, predictable patterns. By exploiting the patterns it is possible to realize enormous savings, both in computer storage and execution time, through avoiding unnecessary arithmetic. GIANT includes an automatic parameter reordering utility. The user, therefore, can construct an input stream in any convenient sequence and subsequently invoke the reordering task to internally reorder the parameters to achieve optimum computational efficiency.

One preliminary step is recommended before invoking the reordering feature. Use DOS to make a copy of the project frame (.FRM) file to a new file of the same (project) name, but with an extension of .ORD. The utility will rearrange the frame specifications in the .ORD file to reflect the outcome of the optimal, reordered sequence. The optimally reordered frame records comprise the .FRM file. When the triangulation task executes, it will look for and, if found, use the .FRM file.
 
By default, the reorder utility will use the .ORD file for its input. If an .ORD file is not found, reorder can use a .FRM file. In either instance, reorder will create a .FRM file. If both .ORD and .FRM files are missing, the project is not qualified by GIANT and will not be offered by the system for any type of processing.

 
Invoke the reorder task with the Alt-R key sequence, or use the mouse to click on the Reorder item of the upper menu bar on the main GIANT screen. No user interaction is required by the utility and the message Computing will flash on the screen to indicate execution of the task. When the task completes, the message clears. The triangulation task may then be run. It is important to note, however, that the reordering task is optional: a successful triangulation does not require use of the reorder feature. As an effective means of expediting the triangulation task, however, the reorder feature is advisable and recommended.

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