ANALYSIS OF OVERLAPS

INTRODUCTION

This appendix describes the process used to carry out the analysis of spatial overlaps for use within the program's 'Analyse Data' and 'Strategy' options.

List of sections:

The Procedure

THE PROCEDURE

The procedure consists of the following stages:

Generate Unique Data

If not already done at this stage, the program generates the unique data based on the true, undivided, cell using the algorithm used in the quick analyses. The total numbers of unique reflections and acentric pairs are determined.

Predict Spots

The spots are predicted within the requested oscillation range or ranges. Each range, at this stage, is padded by the maximum oscillation angle to be used plus a further padding of 3 degrees so that partially recorded spots will be included for all the images to be examined including those at the ends of the oscillation ranges. Spots in the cusp region are excluded and not considered. The included spots are stored in a main overlaps spot list which includes storage of the following data items:

For each oscillation angle ...

Sort Spot List

Sort the spots list in increasing order of the spot 'yd' detector coordintes. Clear counts.

Loop through Phi (oscillation) ranges ...

Loop through images ...

Extract those spots, from the main overlaps spots list, which will be recorded on the current image and store them in the current image list. The data items stored are basically the same as those in the main overlaps spots list with an exta word which stores the position index of the spot in the main list. The overlap flag 1 is set if the spot is found to be spatially overlapped but the overlap 2 flag is not used.

The current image spots list is searched and spatially overlapped spots are flagged (basically the same algorithm as used in the rotation prediction function (RPF) routines used by ROTGEN).

For each spot in the current image spots list, whose central phi value falls within the rotation range for the image, the spatial overlap or spatially non-overlapped flag is set in the main spot overlaps list. Note that this means that, as the images data are accumulated spots may possibly be flagged as both spatially overlapped and non-overlapped. Note also that it is assumed that any spots flagged as non-overlapped can be regarded as non-overlapped from a spot integration point of view and possible overlaps of parts of the spots on adjacant images are ignored.

Accumulate counts of overlapped and non-overlapped spots for all recorded spots.

For the current oscillation angle, sort the main overlaps spot list on the unique indices and then gather the statistics for the percentage of overlaps in terms of the percentages of unique reflections and acentric pairs. A unique reflection is counted as non-overlapped if it is non-overlappped on any of the images in which it is centred. For an acentric pair, both the I+ and I- reflections must be present as non-overlapped spots. The required results are displayed for the oscillation angle in question. If using the standard set of oscillation angles and 5% or more of the spots are found to overlapped, then no more oscillation angles are examined.