Overview

Analysis surfaces perform three functions:

1. Defines the physical extents and location of the grid of pixels on which the analysis is performed

2. Applies a filter to the rays, identifying which rays are included or excluded from the analysis

3. Accumulates the ray quantities into each pixel by either bucket-counting geometric rays for incoherent calculations or sampling the optical field for coherent calculations

The physical extent of the analysis surface can be defined in one of the following ways:

•Automatically sized to the full geometric extent of the positions of selected rays

•Manually sized by specifying the X and Y extent of the outer pixel edges

•Manually sized by specifying the X and Y positions of the outer pixel centers (results in an analysis window are larger by one half pixel per side).

NOTE: When using coherent rays, the user is advised to consider sizing the analysis surface manually by specifying the positions of the outer pixel centers.

Autosizing the analysis surface

When allowing FRED to autosize the analysis surface the geometric extent of the filtered rays determines the analysis surface dimensions regardless of the coherence state of the rays.  In the case of coherent rays the calculated irradiance distribution may be larger in extent than the geometric ray positions.  In this case, the user may opt to leave the sizing automatic use the Scale Factor setting in the analysis surface dialog to increase the dimensions of the analysis surface.

Manual sizing by specifying outer pixel edges

Sizing by specifying the outer pixel edges is most useful for incoherent analysis because the analysis area is directly set and incoherent rays are simply "bucket counted" (ray is counted upon intersection anywhere within the cell).  The pixel pitch is then the width divided by the number of pixels in that direction.

Manual sizing by specifying outer pixel centers

Sizing by specifying the outer pixel centers can be more useful for coherent analysis because the user may want to set the pixel centers for post analysis processing such as a Fourier Transform.  In this case the analysis surface dimensions are larger by half a pixel on each side.  The pitch of the pixels in this case is the width divided by the number of pixels minus 1 and the analysis surface width is the number of pixels times the pixel pitch..