Get Grid Peak Locations

Use the Get Grid Peak Locations dialog options (E3PEAKS GX) to automatically select solution picks from a grid.

The peak locations are selected using a grid peak-picking algorithm, are stored in the current database and are displayed as symbols on the current map.

Locate Grid Peaks dialog options

Input grid

Choose a grid from which solutions are to be selected. When using magnetic data, an analytic signal grid is required. When using EM-61 data, the grid may be either the top channel, the bottom channel or the difference channel

Script Parameter: E3PEAKS.GRID

Output database
(.gdb)

Output database file name.

The solution database is no longer deleted and re-created each time, since it is now possible to store multiple solution sets to the same database. 

Script Parameter: EULER3D.SOLDB

Line for peak locations

The Name of the "group" line to save X, Y locations.

Script Parameter: EULER3D.XYSOLGRP

Channel for grid
values

The grid values at the peak locations are written to this channel

Script Parameter: E3PEAKS.CHAN

No. of passes of 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

Script Parameter: E3PEAKS.PASS

Level of peak
detection

The Blakely method is used to find peaks in a grid. For each grid cell, the GX compares its value with the values of its eight (8) nearest grid cells in four directions (along the row, along the column, and along both diagonals). There are four sensitivity levels which may be used to determine whether a grid cell will be selected as a peak:

Normal (4) - grid values in all of the 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.

Script Parameter: E3PEAKS.BLAKELY

Grid value
cut-off level

Specify a grid value below which you want peaks to be removed from the list. Leave the entry blank to include all of the located solutions.

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

If you select all of the solutions, you have the option to window these later using the ‘Window results…’ menu option

Script Parameter: E3PEAKS.CUTOFF

[Symbol]

Select the Symbol button to define (or re-define) the symbol for plotting.

Application Notes

Output 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.