Grid Outline

Use the Grid and Image > Utilities > Grid Outline menu option (GX: GRID2PLY) to detect edge points in a grid image. You can either save the detected edges to a polygon file or draw them directly on the current map.

Grid Outline dialog options

Grid file

The name of the grid file from which to extract edge points.

Script Parameter: GRID2PLY.GRID

Action

Choose how to output the detected edge:

Draw on current map — draws the polygon on the active map.
Save to a file — saves the edge coordinates to a polygon (.ply) file.

The next dialog depends on which action you select.

Script Parameter: GRID2PLY.ACTION

(If the first letter is "D", the polygon is drawn to the current map.)

Minimum polygon size (points)

Specifies the minimum number of points a polygon must have to be included.

Default: 0 points (includes all polygons).
This option is useful for very large grids with many small “island” polygons, as it ignores polygons with fewer than x points.

Script Parameter: GRID2PLY.MINPOINTS

Save Edges to a Polygon File

Polygon file name (.ply)

The name of the polygon (.ply) file to create or update.

Script Parameter: GRID2PLY.PLY

Save mode

Choose how to save the polygon data:

New file — create a new polygon file.
Append — add the polygons to an existing file.

Script Parameter: GRID2PLY.MODE

Edge resolution (cells)

Controls thinning of edge points.

Default: 1 cell (no thinning).
Values > 1 thin the edge to produce a coarser polygon.

Script Parameter: GRID2PLY.EDGERES (Default 1.0)

Draw Grid Edge on the Map

Line colour	Select the line colour for the edge. Script Parameter: GRID2PLY.LCOLOR
Fill colour	Select the fill colour for the polygon. Script Parameter: GRID2PLY.FCOLOR
Line thickness (mm)	Specify the thickness of the drawn edge line in millimetres. Script Parameter: GRID2PLY.THICK
Line style	Choose a line style from the list. Script Parameter: GRID2PLY.STYLE
Style pitch (mm)	Specify the style pitch for patterned line styles. Script Parameter: GRID2PLY.PITCH
Edge resolution (cells)	Enter the edge-thinning resolution for map output, in millimetres. Default: 0.2 mm Set to a negative value to disable thinning. This option reduces rendering size for complex edges at large scales. Script Parameter: GRID2PLY.EDGERESMAP (Default 0.2)

Application Notes

Only the outer boundary of the first non-dummy grid region is outlined.
Holes and interior islands are not detected.

If the grid outline is saved to a polygon file, it may be used for:

Masking operations
Drawing on maps using POLYDRAW GX
Use by external programs

The Edge resolution parameter controls thinning by removing colinear points below the specified resolution, producing a coarser edge.

For map output, thinning is disabled when the value is less than 0.0.
For file output, thinning is applied only if the resolution is greater than the grid’s X cell size.