Three-Dimensional Projection Matching: a method of refinement in reconstructing single particles from their projections [Penczek et al., 1994]. A preliminary 3D map, obtained by random-conical reconstruction or angular reconstitution, is used to compute 'predicted projections' on a grid in angular space, which are held in the computer memory. One by one, the experimental projections are now compared (by cross-correlation, See CCF) with the set of predicted projections, to find the best Eulerian angles representing their projection direction. Next, a refined 3D map is computed, and again this is used to compute 'predicted projections,' etc. For self-consistent, homogeneous data sets, this procedure converges in a higher-resolution 3D map.

 

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Projection Cutting: Any method of printing in which the image is optically projected on the sensitized material.

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Matching Principle: The concept that all costs and expenses incurred in generating revenues must be recognized in the same reporting period as the related revenues.