Grid Peaks

Use the Grid and Image > Utilities > Grid Peaks menu option (GRIDPEAK GX) to find peaks in a grid file.

Grid Peaks dialog options

Grid to find peaks	Input grid to find peaks Script Parameter: GRIDPEAK.GRIDIN
No. of passes of smoothing filter	Number of passes of smoothing (Hanning) filter. Default is 0. Script Parameter: GRIDPEAK.PASS
Level of peak detection	Level of peak detection "Blakely test" (see below) (Default is Normal). Script Parameter: GRIDPEAK.BLAKELY
Grid value cut-off level	Grid value cut-off level Script Parameter: GRIDPEAK.CUTOFF
Line to save refined target list	Output LINE number (Default is D10). Only Random-type lines (those beginning with "D") are presented in this list. Script Parameter: GRIDPEAK.LINE

Application Notes

Smoothing Filter

Specify the number of passes of smoothing (Hanning) filter to apply to the grid so that low amplitude, high frequency ‘noise’ targets, will not be picked. The grid will not be smoothed if you enter 0 (zero) or leave the entry blank. More filter passes tend to reduce the number of peaks found. The default is to apply the filter 3 times.

The system applies 9-point (3x3) Hanning smoothing filter to the grid, if smoothing is desired. The coefficients of the filter are:

0.06 0.10 0.06

0.10 0.36 0.10

0.06 0.10 0.06

Level of Peak Detection - Blakely Test

This GX uses Blakely's method¹ to find peaks in a grid. For each grid cell to be considered, the GX compares its value with values of eight (8) nearest grid cells in four directions (along the row, column, and both diagonals). There are four levels to determine whether a grid cell can be selected as a peak:

Normal (4)	Grid values in all nearest grid cells are lower.
More peaks (3)	Grid values in any three directions are lower.
Even more peaks (2)	Grid values in any two directions are lower.
All ridge peaks (1)	Grid values in one direction are lower
Selecting Normal (4) (Default) finds fewer peaks. To find all ridges, use All ridge peaks (1) option.

Grid Value Cutoff Value

Specify a grid value below which you want peaks to be removed from the list. Leave blank to include all targets found.

You can determine a reasonable cut-off level by examining the grid using the image tool or the related colour bar.

Output Lines and Channels

The X and Y coordinates of the selected peaks are placed in the X and Y channels respectively in the specified line. The grid values at the peak locations used to pick the locations are placed in the specified grid value channel (if grid smoothing is selected these will be the smoothed values). A Target_ID channel is also created, and peaks are numbered sequentially, beginning at 1.

Reference