Preparation of the Frame File

2.1.2 Preparation of the Frame File

The frame file contains the approximate positions and attitudes, along with estimates of their standard deviations, for each frame on which images have been measured. The position and attitude standard deviations must reflect the precision to which the information is known. For instance, suppose that kinematic GPS had been used to determine the coordinates of the exposure stations for some of the frames in a project, while the remaining frame exposure station coordinates were scaled from a topographic map. The standard deviations for the GPS-derived exposure station coordinates might be set to 0.01 (one one-hundredth seconds of arc, approximately 30 centimeters on the surface) while the topographic map-derived coordinates are assigned a standard deviation of 30.0 (thirty seconds of arc, approximately 1 kilometer on the surface). Since kinematic GPS does not currently provide useful attitude information, a value of 900000.0 (ninety degrees) might be appropriate for all of the orientation angles. Refer back to the introduction of this chapter for the explanation of the angle specification format used in this example, if necessary. The frame file derives its name from the name of the project and has an extension of .FRM or .ORD, as discussed in the box below.

It is important when preparing the Frame File to have a very clear sense of the coordinate system that is being used in the triangulation. In classical aerial photogrammetry the coordinate system is well known. Using an ellipsoid as the vertical datum gives rise to the well-known coordinates of latitude, longitude and height. For spatial orientation of the frame, an auxiliary Cartesian coordinate system whose origin is at the nadir point of the exposure, is introduced. In this auxiliary system the primary rotation is named Omega and occurs around the X axis which is positive East. The secondary rotation is named Phi and occurs around the Y axis, positive North. The tertiary rotation angle, Kappa, occurs around an upward-positive Z axis. All three angles are positive in an anti-clockwise direction, when viewed from the coordinate system's origin outwardly along the axis.

In less conventional settings such as those commonly encountered in close-range or industrial photogrammetric triangulation problems the coordinate systems may not be as well-known. While rectangular coordinate systems are generally used, it is not a formal requirement. The critical aspect of any coordinate system definition is that the primary rotation always be around the first or X axis, the secondary rotation about the second or Y axis and the tertiary rotation about the third or Z axis. The contents of the Frame File must observe these relations for the triangulation to adjust correctly.

Structurally, the Frame File consists of pairs of records for each frame: the number of records in the Frame File should always be an even number that is twice the number of frames in the project. There is no limit to the number of frames in a project. The first record contains the frame name, the three exposure station coordinates and the optional standard deviations of each of the three coordinates. A flag permits the constraint of any or all of the position coordinates. Definitions of the flag's values are shown in the following table. Specifically, in a project using a geographic coordinate system, the first frame record of the pair would contain the frame name, longitude, latitude, height, standard deviation of longitude, standard deviation of latitude, standard deviation of height. For a project employing a rectangular coordinate system the record would contain, frame name, X, Y, Z, standard deviation of X, standard deviation of Y, standard deviation of Z.

Flag	First Field	Second Field	Third Field
0	Unknown	Unknown	Unknown
1	Known	Unknown	Unknown
2	Unknown	Known	Unknown
3	Known	Known	Unknown
4	Unknown	Unknown	Known
5	Known	Unknown	Known
6	Unknown	Known	Known
7	Known	Known	Known

The second record of the frame pair contains the orientation information about the frame. The frame name is again repeated in the first field, followed by the primary, secondary, tertiary rotations, and, optionally, the standard deviations of the three rotations. A flag in the final field of the record permits the constraint of specific attitude angles similar to the above table for position coordinate constraints. Referring to the two illustrations in the previous paragraph, the second record would contain the frame name, Omega, Phi, Kappa, standard deviation of Omega, standard deviation of Phi, standard deviation of Kappa for the geographic instance; rotation about X, rotation about Y, rotation about Z, standard deviation of X rotation, standard deviation of Y rotation and standard deviation of Z rotation for the rectangular coordinate system.

The tables below identify the precise formats of the frame record pair in respective order.

Field	Contents	Data Type	Columns
1	Frame Name	Alpha-Numeric	1-8
2	First Axis Coordinate	Floating Point	9-20
3	Second Axis Coordinate	Floating Point	21-32
4	Third Axis Coordinate	Floating Point	33-44
5 Optional	Standard Deviation of First Coordinate	Floating Point	45-54
6 Optional	Standard Deviation of Second Coordinate	Floating Point	55-64
7 Optional	Standard Deviation of Third Coordinate	Floating Point	65-74
8	Constraint Flag	Integer	80

Field	Contents	Data Type	Columns
1	Frame Name	Alpha-Numeric	1-8
2	Primary Rotation	Floating Point	9-20
3	Secondary Rotation	Floating Point	21-32
4	Tertiary Rotation	Floating Point	33-44
5 Optional	Standard Deviation of Primary Rotation	Floating Point	45-54
6 Optional	Standard Deviation of Secondary Rotation	Floating Point	55-64
7 Optional	Standard Deviation of Tertiary Rotation	Floating Point	65-74
8	Constraint Flag	Integer	80

A word about units is necessary. The units used for data in the Frame File must correspond to the units used in the Ground Control File, described below in Section 3.2.2. For geographic coordinate systems used in conventional mapping work, exposure station position and orientation are described using the compressed DMS angular representation illustrated above. For rectangular coordinate systems, exposure station coordinates can be specified in either feet or meters; orientation for rectangular coordinate systems must be specified in the compressed DMS format. Often, special close range photogrammetric work may find other units, say millimeters, more convenient or contextual. GIANT can accept such units. The user must exercise caution, however, to ensure a consistency of units when preparing the input data stream.

2.1.2.1 Verification of the Frame File

GIANT offers a facility for automatically checking the structural integrity of a project's frame file. It is recommended that this feature be exercised as a first-order means of data validation before executing the triangulation adjustment. The verification feature is accessed from the main GIANT Process Options screen. If the project of interest is not displayed in the Project field, use the Browser button and Path field to select the appropriate project. (Section 3.1 gives detailed instructions for using the Browser, Path and Project features of the Process Options screen). Use the mouse or Alt-V key combination to select the Verify menu option. A pull-down menu then appears. Selection of the Order file or Frames file option will invoke the file verification procedure.

The verification procedure conducts the following three integrity checks on the structure of the Order or Frames File.

Blank records.
Records out of order: position record, attitude record sequence violated.
Duplicate frame names.

Failure to meet the checks is identified by a pop-up message that alerts the user to the failed condition(s). Upon notification of such an integrity check failure, exit GIANT and use a text editor to correct the identified condition(s) in the dataset. When the corrections have been made, re-start GIANT and repeat the verification test. Continue this iterative correction phase until the verification executes without failure. Do not attempt to execute the triangulation adjustment with known errors in the input data stream. Doing so will only result in an abnormal termination of the program.

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