Surfer imports and exports Golden Software Blanking Files .BLN.
Golden Software Blanking File .BLN is an ASCII format file used to store geographic information including polygons, polylines, and points. Spatial information is only concerned with the location of objects in space (i.e., their coordinates) and not with their attributes (i.e. line or fill style, marker symbol used, text labels, etc.). Even though the primary use of GS Blanking files is to indicate regions of a grid file to be assigned the NoData value, they can also be used for simple boundaries and decorative illustrations.
The general format of the file is:
length,flag "Pname 1"
length,flag "Pname 2"
The length value is an integer which indicates the number of X, Y coordinate pairs that follow.
The flag value is 1 if the region inside areas is to be assigned the NoData value and 0 if the region outside areas is to be assigned the NoData value.
Pname is optional and is the name of a primary ID to be associated with the object. The primary ID is used to link the object to external data.
X, Y Coordinates
Following lines contain the actual X, Y coordinate pairs that make up the object. These can be integers or real numbers, and are stored 1 pair per line.
Type of Object
The type of object is determined as follows:
If the type/length field is 1, the object is considered a point. One coordinate pair follows.
If the type/length field is greater than 1 and the first and last coordinate pairs are equal, the object is considered a simple closed polygon. Otherwise, the object is considered a polyline.
The first ID attribute for all polyline, polygon, and symbol objects are automatically exported to all .BLN files. For contour maps, the elevation is exported as the "STD_ID1" attribute for all polylines in the contour map. If a different attribute other than the first listed attribute for objects is desired, rename the desired attribute to "STD_ID1". This named attribute will be used instead of the first attribute listed on the Info tab. The color, size, symbol shape, width, and other properties are not exported.
This example shows a simple .BLN file, with a single polygon:
This example shows a single complex polygon .BLN file, with an island. Note the 48,99 coordinate pair starts the first polygon (line 2), closes the first polygon (line 8), and closes the entire complex polygon (line 14). The 40,70 coordinate pair starts (line 9) and closes (line 13) the sub-object within the complex polygon. Each sub-object in a complex polygon is followed by the first polygon coordinate pair:
Loading a BLN
Use the File | Open or the Open Data dialog (i.e. Home | New Map | Base, Home | New Map | Post) to load a .BLN file.
Import Options Dialog
No import options dialog is displayed.
Import Automation Options
No import options are available.
Saving a BLN
Export Options Dialog
Export Automation Options