extracted might be displayed or used by some automated process. There are many such automated image exploitation processes, including:
1. Image resampling to produce an orthorectified image
2. Automated image matching
Note: Most persons not familiar with image exploitation assume that transforming image to ground coordinates is most frequently used. In practice, transforming ground to image coordinates
is more frequently used, especially in stereoscopic image exploitation.
3.1.3. Output Coordinates Accuracy Data
In addition to producing ground or image coordinates, the ICT Services should output data describing the position accuracy of these output coordinates. Position accuracy output data is not
useful in all image exploitation operations, and may be rarely needed for image coordinates. However, accuracy data should be automatically produced whenever it is needed by the current
image exploitation operation.
This accuracy data should take the form of position error statistical estimates. Absolute error estimates should be available for single points, relative to the defined coordinate SRS. Relative
error estimates should be available for pairs of points. These error estimates should be in the form of covariance matrices, as defined and specified in Abstract Specification Topic 9: Quality.
3.1.3.1. Output Accuracy Determination Error estimates for coordinates output from a transformation should represent the combination of
all significant error sources or error components. In general, three types of error sources need to be considered: input coordinate errors, transformation parameter errors, and transformation
computation errors.
The input coordinates used by the transformation will often contain errors, which propagate to the output coordinates. Error estimates for the input coordinates can be propagated to the resulting
output error estimates by using the partial derivatives of the individual output coordinates with respect to the individual input coordinates.
The transformation parameters used will often contain errors, which propagate to the output coordinates. Error estimates for the transformation parameters can be propagated to the resulting
output error estimates by using the partial derivatives of the individual output coordinates with respect to the individual transformation parameters.
The transformation computations will sometimes introduce significant errors, at several steps in the computation, which propagate to the output coordinates. Typical computation errors can be
propagated to the resulting output error estimates by using the partial derivatives of the individual output coordinates with respect to the internal quantities where errors are committed.
3.1.3.2. Input Coordinates Accuracy Data In order to produce output coordinates accuracy data, the ICT Services will usually need similar
accuracy data for the input coordinates. For image coordinates, this input accuracy data should reflect the estimated errors in determining the correct image position. In some cases, the proper
image coordinates error estimates will be zero.
3.1.3.3. Coordinate Transformation Accuracy Data To produce output coordinates position accuracy data, the ICT Services will also generally need
accuracy data for the transformation performed. This transformation accuracy data might be for the transformation as a whole, or for the various parameters used in the transformation.
A transformation between ground and image coordinates will have non-zero errors, except for synthetic images. A coordinate transformation between two different image versions will often
have zero error estimates, except for computation errors. A coordinate transformation between different ground SRSs will sometimes have significant errors. However, ground coordinate
“conversions” will have zero error estimates, except for computation errors.
Computation errors might or might not be negligible even when double precision floating point arithmetic is used in coordinate transformations. For example, the 48 bit precision of a double
precision floating point number applied to a longitude of about 180 degrees corresponds to an error of about 8 micrometers. In performing coordinate transformation, several such errors can be
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committed. Although very rare, some ground coordinates could have similar size errors from all other sources.
Data about the inherent accuracy of a coordinate transformation should be recorded as metadata for that transformation. Data about the computation error in an implementation of a coordinate
transformation could be either internal data of the implementation or metadata about that implementation.
3.1.4. Handle Image Versions
