Invoke the Image File Verification with the Alt-V key sequence or use the mouse to click on the Verify option of the upper menu bar of the GIANT main Process Options screen. A drop-down menu will offer the various verification tasks available. Select Image File using the mouse. The image file verification procedure scans the image file corresponding to the currently selected project (the project shown in the Project field of the Process Options screen) for violations to the following conditions:
The verification procedure alerts the user of a violation through a pop-up window. The pop-up window will contain a field indicating the specific violation and the record, image or frame responsible. An arrow to the right of the window permits the user to view, in turn, all violations in the file, if more than one are found.
The user is advised to take note of the violation(s), and to correct the image file using a text editor before attempting to execute the triangulation procedure. After correcting the violating condition it is also advisable to re-run the verification procedure to ensure that the violation was in fact corrected, and that no new errors have been introduced.Invoke the Frame File Verification with the Alt-V key sequence or use the mouse to click on the Verify option of the upper menu bar of the GIANT main Process Options screen. A drop-down menu will offer the various verification tasks available. Select Frame File using the mouse. The frame file verification procedure scans the frame file corresponding to the currently selected project (the project shown in the Project field of the Process Options screen) for violations to the following conditions:
The verification procedure alerts the user of a violation through a pop-up window. The pop-up window will contain a field indicating the specific violation and the record or frame responsible. An arrow to the right of the window permits the user to view, in turn, all violations in the file, if more than one is found. The user is advised to take note of the violation(s), and to correct the frame file using a text editor before attempting to execute the triangulation procedure. After correcting the violating condition it is also advisable to re-run the verification procedure to ensure that the violation was in fact corrected, and that no new errors have been introduced.
Invoke the Control File Verification with the Alt-V key sequence or use the mouse to click on the Verify option of the upper menu bar of the GIANT main Process Options screen. A drop-down menu will offer the various verification tasks available. Select Control File using the mouse. The control file verification procedure scans the control file corresponding to the currently selected project (the project shown in the Project field of the Process Options screen) for violations to the following conditions:
The verification procedure alerts the user of a violation through a pop-up window. The pop-up window will contain a field indicating the specific violation and the record or control point responsible. An arrow to the right of the window permits the user to view, in turn, all violations in the file, if more than one are found. The user is advised to take note of the violation(s), and to correct the ground control file using a text editor before attempting to execute the triangulation procedure. After correcting the violating condition it is also advisable to re-run the verification procedure to ensure that the violation was in fact corrected, and that no new errors have been introduced.
Further validation of the input stream can be gained by executing GIANT in the intersection mode. The intersection mode is based on the most fundamental photogrammetric premise: if the spatial position and orientation of a frame are known, then object space coordinates can be directly computed from image measurements using simple intersection calculations of analytic geometry. Of course, the purpose of the triangulation is to precisely determine the spatial locations and orientations of the frames. However, with kinematic GPS now available it often happens that, even before the adjustment, reliable information about a frame's absolute orientation is available. Even if kinematic GPS information is not available, the estimates of frame orientation can be used for this test.
To execute a data stream validation using the Intersection option, configure GIANT according to the project's requirements. On the Process Options screen is a switch labeled Mode, which has two options, Intersection and Triangulation. Use the mouse to set the switch to Intersection Mode. Start the execution of the task with the Compute button found at the bottom of the display. While the task is executing, it flashes the message Computing. When the message disappears, the task is complete. Exit GIANT and, using a standard text editor, examine the residuals in the output listing. The magnitudes of the residuals will depend, in part, upon the precision to which the frame orientations were known: the less precise the orientation, the larger residuals. Residuals of anomalous magnitude, in comparison to the others, may indicate a problem. If the residual pertains to a point that is a control point, it may be prudent to inspect the ground control file and confirm that the point's ground coordinates have been entered correctly and that its name has been correctly specified. If there is no apparent problem in the ground control file, examine the image file. The residual listing will identify the frames on which the anomalous image residuals appear. Generally speaking, it is difficult to debug the coordinates in the image file, but coarse measurements with a scale or ruler might indicate that the frame/point combination in the image file is misidentified. Anomalous residuals of all points imaged on a specific frame may suggest an error in the frame file. Continue the analysis of the anomalous residuals in this manner. If corrections are made to any of the image, frame or ground control files it is advisable to repeat the corresponding verification test, followed by a repeat of the intersection test.
Successful completion of all validation tests does not guarantee a correct or successful triangulation adjustment. It does help to prevent time from being wasted in waiting for an adjustment that ultimately terminates abnormally because of mistakes in the input data stream.
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