.BLN blanking files are used to represent boundary information and are also used for blanking polygonal regions within grids. Blanking files are comma-delimited ASCII files consisting of a repeating series of polygon, polyline, or point definitions. Each definition has the following format:
|
npts, flag |
This is the header for the first boundary in the blanking file.
npts: The number of XY coordinate pairs used to define this boundary.
flag: Defines the type of blanking. If you are using this boundary as a blanking file, a value of 0 is used to blank outside the defined boundary, a value of 1 blanks inside the defined boundary. |
|
x1, y1 |
first coordinate pair of the boundary |
|
x2, y2 |
second coordinate pair |
|
... |
coordinate pairs |
|
xn, yn |
This is the last coordinate pair of the boundary. For a closed polygon, this point must be identical to the first coordinate pair. |
The sequence may be repeated any number of times within the same file to define multiple polygons and polylines. When using multiple polylines in a blanking operation, the flag value in the polygon header should be 1 for all boundaries; otherwise, the entire grid is blanked. If you need to blank outside of multiple polygons, create a composite polygon to avoid blanking the entire grid.
The blanking flag parameter is used to determine blanking inside (1) or blanking outside (0). The XY coordinates used in the blanking file are in the same units used for the XY coordinates in the grid file.
An optional Z coordinate may be specified after the X and Y coordinates when using a .BLN file for breaklines in Surfer. The Z value is required for breaklines.
The following example defines two breaklines:
2, 1
3.0, 4.5, 1.0
0.5, 4.5, 2.0
3, 1
4.5, 0.0, 1.1
8.5, 0.0, 1.2
8.5, 1.5, 1.4
The following example defines one fault:
2, 1
1.5, 1.0
7.5, 8.5
The following example defines one closed polygon.
5, 0
1.0, 1.0
1.0, 6.0
6.0, 6.0
6.0, 1.0
1.0, 1.0
The following example defines a complex polygon, with three sub-polygons:
17, 0
1, 1
1, 2
2, 2
2, 1
1, 1
3, 3
3, 4
4, 4
4, 3
3, 3
1, 1
7, 5
7, 6
8, 6
8, 5
7, 5
1, 1
See Also