The intermediate results from *CROSS-CORR* can be used to monitor
the geometric/photometric state of the raw science image. In the vector
displacements (VD) file, these intermediate results are stored in a
binary table extension containing the following output for each
sampling position:

- 1.
- science image x-position (sample),
- 2.
- science image y-position (line),
- 3.
- ITF x-position of best match (sub-pixel accuracy),
- 4.
- ITF y-position of best match (sub-pixel accuracy),
- 5.
- maximum cross-correlation coefficient (computed for pixel location accuracy),
- 6.
- number of pixels used to calculate the correlation, and
- 7.
- the ITF level used for
*CROSS-CORR*

The total number of entries in the binary table extension is both camera
and dispersion dependent. Table 5.1 contains the number of
fiducial locations used in *CROSS-CORR*.

Number of Locations | ||

Camera | Low Dispersion | High Dispersion |

LWP | 150 | 490 |

LWR | 151 | 511 |

SWP | 139 | 510 |

The data contained in the binary table extension can be used to
produce diagnostic plots for *CROSS-CORR*. Panel *a* of
Figure 5.1 shows the displacements computed between an SWP
low-dispersion image and the SWP ITF. The small boxes denote the
fiducial locations where a successful correlation was determined. The
associated vector represents the computed displacement between the raw
science image and the ITF; the vector displacements have been magnified
for visual clarity. Single points mark the locations of fiducials with
unsuccessful correlations. Panel *b* of Figure 5.1 shows the
magnitude of the correlation coefficients corresponding to the results
in Panel *a*. Larger plus signs denote stronger correlations. The
dashed lines represent the region of the image that is photometrically
corrected. Recall that all of these correlations have passed the 1%
probability distribution test which means that there is less than a 1%
probability any of these correlations could have arisen by random
chance. The corresponding example for high-dispersion data is
illustrated in Figure

**Figure 5.1:**
(*a*) Displacements computed between an SWP
low-dispersion image and the SWP ITF. (*b*) Magnitude of the
correlation coefficients corresponding to the results shown in
Panel *a*.

** Figure 5.2: **
(*a*) Displacements computed between an SWP
high-dispersion image and the SWP ITF. (*b*) Magnitude of the
correlation coefficients corresponding to the results shown in
Panel *a*.