Edit Grid Inside Polygon (NGAPOLYSM)

The GM-SYS 3D Tools > Grid Editing > Edit Grid Inside Polygon option replaces the area inside of a polygon with a 0-, 1st-, 2nd-, or 3rd-order polynomial trend surface, a minimum curvature surface, or a user-defined expression. The polynomial surface may be based on all points, or edge points only.

Edit Grid Inside Polygon Options

Input grid file	The grid to be modified
Polygon file	An existing polygon file that overlaps a portion of the grid to be masked.
Calculate surface using	Define trend surface using EDGE points, ALL points, Minimum Curvature, or an EXPRESSION. Default is EDGE.
Smooth surface order	Data within the polygon will be smoothed to a surface of this order: 0 to 3. (Not used in the EXPRESSION mode.)
Auto rezone	Select "Yes" or "No". If affirmative, new grid statistics are generated after the edit and the grid rezoned using the colour method and colour table selected below. If no, the map is redrawn using the old statistics.
Colour method	Select the colour method. If the selected colour scheme is an .itr file or a .zon file, the colours are already attributed to data ranges, and this entry remains disabled. The colour method can be one of: As last displayed Default Histogram equalization Normal distribution Linear Log-linear The method "As last displayed", will display each grid as it was displayed the last time the grid was viewed, and the colour tables will be ignored.
Colour table	Select a colour table. (TBL, ZON, AGG or ITR assumed)
[View Poly]	Draws the selected polygon on the current map.
[Erase Poly]	Erases the selected polygon on the current map.
[Undo]	Click to undo the previous grid edit - one level back only.

Expression - Fill a Polygon

Grid file G1	Grid file name of the variable G1. G1 is required.
G2	Grid file name of the variable G2.
G3	Grid file name of the variable G3.
G4	Grid file name of the variable G4.
G5	Grid file name of the variable G5.
G6	Grid file name of the variable G6.
Expression g1 = OR	Enter the right side of an expression for setting grid values inside the polygon.
Expression file	OR name of an expression file (.EXP).

Application Notes

Expression Examples:

g1 = 1000 (set all the cells inside the polygon to "1000");

g1 = g1 * 2 + 500 + sqrt(g1);

g1 = (g2>g3)?g3:g2;

Grid file 1 is required. If grid G2 to G6 do not exist, they will be created based on the grid G1.

If an expression file is specified, it will be read as the expression and any expression that was defined will be ignored. Each line of the expression file must end with a ";" will be concatenated to form the expression. The maximum expression length is 1023 characters.

"Undo" will recover the most recent edit of the grid.

The Minimum Curvature option uses the public-domain GX "USGS_GRIDPLUG.GX" written by Jeff Phillips and documented in "Open-File Report 03-010".