The application cnetref finds the best reference for a Control Point based on user specified Criteria.

Application takes in as input the Control Net CNET and its corresponding images list FROMLIST. FROMLIST contains the filenames of all the images that are part of the input Control Net.

The resulting output Control Net is placed in the user specified file ONET. The Id and Description for the output Control Net can be specified in NETWORKID and DESCRIPTION parameters respectively. If the values are not entered then the information is taken from the input Control Net.

Best Reference for the Control Point can be chosen based on the following four CRITERIAs. For all the criterias, picking the best Reference is skipped if the Control Point is not Free or if either the Control Point or the Reference is EditLocked.

1. EMISSION : Of all the valid Control Measures in a Control Point, the Control Measure with the least Emission Angle will be chosen as the Reference.

2. INCIDENCE: Of all the valid Control Measures in a Control Point, the Control Measure with the least Incidence Angle will be chosen as the Reference.

3. RESOLUTION: Of all the valid Control Measures in a Control Point, the Control Measure with the best Resolution TYPE will be chosen as the Reference. All the images in the Control Net must have the resolution in the same units.
The best Resolution can be chosen from the following TYPEs:
a. HIGH - The Control Measure with the Highest Resolution will be chosen as the Reference.
b. LOW - The Control Measure with the Least Resolution will be chosen as the Reference.
c. MEAN - The Mean Resolution is calculated from the Resolution all the images within each Control Point. The Control Measure closest to the Mean Resolution will be chosen as the Reference.
d. NEAREST - The Control Measure with the Resolution closest to this user specified value in RESVALUE will be chosen as the Reference.
e. RANGE - The first Control Measure in the MINRES - MAXRES Range will be chosen as the Reference.

4. INTEREST: Of all the valid Control Measures in a Control Point, the Control Measure with the best Interest will be chosen as the Reference. This option uses an interest operator to find the most interesting point in the area near each Control Point of a Control Net. The area is defined by the keywords DeltaLine and DeltaSample. The application starts by finding the best Interest for each valid Control Measure in a Control Point. Then the Control Measure with the best Interest among all the valid Control Measures in the Control Point is chosen as the Reference. After the new Reference is chosen, all the Control Measures are aligned to the new Reference's location. The movement of the Control Point can be limited to the Overlaps by enabling LIMIT and entering the list in OVERLAPLIST. The Overlaplist contains the Serial Number and their intersections. The intersections information can be got from the application findimageoverlaps. If an exact match of the Control Measure's Serial Number in the overlaplist fails then this option finds image overlaps by getting intersection of the individual image footprints. If the overlapslist is not specified, then the Point can be moved in the area defined by DeltaLine and DeltaSample.

The Interest operator reads in a chip of size Delta Samples and Lines from each Control Measure(Cube) in a point. If the Overlap list is included then the overlap polygon is taken into consideration when the chip reads the cube. For each pixel in the chip, it extracts a sub chip of box size (Samples, Lines) around the pixel. It first checks the pixel for validity as specified in the DEFFILE. If the pixel passes the above tests, then the Interest is calculated for the box around the pixel using the chosen algorithm. This way it calculates the interest for all the pixels in the chosen area (chip) around the Control Measure and the best Interest (highest value) is chosen among them. The best Interest is calculated for all the Control Measures in a Control Point.
The application then selects the best Interest of all the valid Control Measures in the Control Point and chooses it as the Reference. It then moves all the other valid Control Measures to the chosen Reference by mapping the Reference Lat/Lon to a sample, line in the Control Measure. It then creates a new Control Net using these new "more interesting" Control Points. If the BestReferenceIndex is not calculated because no Interest was calculated for all the Control Measures or if the BestReferenceIndex's Interest is invalid(less than the threshold Interest) then the Control Point is set to be ignored.

Interest Algorithm could be:
1. Standard Deviation
2. Gradient

The options for the Interest Operator is defined in PVL group in the DEFFILE. The DEFFILE should have the Operator Group relevant for the Interest Operator plugin. It defines the algorithm(Name) to be used to calculate the interest, the box size (Samples, Lines) and the distance (DeltaSamp, DeltaLine) the algorithm is allowed to move the point from the current position. It defines the minimum interest (MinimumInterest) value for the interest to be considered a best interest. If the point must be static then set the DeltaSamp and DeltaLine to zero.
All the keywords in the Operator Group are required for this Criteria.
Example:

Note:
1.If Control Measures with no camera is encountered, then the application is halted and no ouput Control Net is generated.
2. The values Samples, Lines, DeltaLine, DeltaSamp, MinimumInterest for the Operator are entirely dependent on the images in the Control Net. Recommended preprocessing would be to run "gradient" filter or "svfilter" and run "hist" to get the image stats and set the values for the Operator accordingly.

For all the criterias except Interest, the application first validates each measure for the properties specified in the "ValidMeasure" PvlGroup in DEFFILE. The Validity test is optional for all the Criterias.

Validation is little different if using the Interest Critera. The Interest Operator while finding Interest for a Valid Control Measure, first Validates each Sample, Line location in the DeltaSample, DeltaLine area of the Control Measure and then calculates the Interest for that location. This way the expensive Interest calculation is bypassed for an invalid Sample, Line location. Validity test is also performed after moving the Control Measure to the new location of the BestReference chosen after the Interest operation for all the Control Measures in the Control Point. If the moved Control Measure fails the Validity test, then it is set to be Ignored.

Following is the format for the Pvl DEFFILE file with the defaults for Control Measure validation:

If the Control Measure does not pass the validity test, then it will be be Ignored. If the number of Valid Control Measures in a Control Point is less than 2, then the Control Point is Ignored.

If the "Required" parameters are not entered or misspelled, then the application will throw an error. If "Optional" parameters are not entered then the Control Measure will not be validated against that option.

The entire Control Net processing can be logged in an output LOG file. Log information such as Control Point and Control Measure details and change statistics are placed in LOG file if specified in PVL. Following is the format of the Log File: