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How do I create a BLN file for use in Raster Tools?

This article describes how to create a BLN file for use as a fault or breakline in Raster Tools.
 
You can create a BLN file in a number of different applications, such as Surfer, Notepad, and Excel. A BLN file is a worksheet file that consists of a one line header followed by a list of XY points. The BLN file can contain multiple points, lines, or polygons that are separated by a header row.

The one line header simply is the number of proceeding data points. If you are using the BLN file for blanking a grid, then the header will also need to contain a 1 or a 0 (the blanking flag number). A 1 means to blank inside the boundary and a 0 means to blank outside the boundary. If you are not using the BLN file for blanking, then it doesn’t matter if you have a 1 or a 0.

See also the Surfer webinar: Creating and Editing BLN files for Blanking Maps in Surfer

To create a BLN file:

The simplest method to create a BLN file is to enter the coordinates directly into a worksheet program like Surfer's worksheet or Excel. This works well if you know the coordinates for the objects you want to describe in the BLN file.

If you have 1 data point in your BLN file, then you are creating a point location. If you have 2 or more data points, then this will be described as a line. If you have multiple data points, and the first and last coordinate set are the same, then this is a polygon. For example:

A BLN file with two points:

1
5,6
1
4,3


A BLN file with two points and one polyline (made of three points connected together):

1
5,6
1
4,3
3
1,1
4,2
6,5


A BLN file with two points, one polyline, and one polygon:

1
5,6
1
4,3
3
1,1
4,2
6,5
5
0,0
5,0
3,4
1,4
0,0

This will look like:

 

A BLN file with one polygon:

5,0
0,0
5,0
3,4
1,4
0,0

You can enter these coordinates in the Surfer worksheet and then click File | Save As to save it to a BLN file. If using Notepad or WordPad, you can simply save to filename.bln. If using Excel, you can save the worksheet to TXT format and then rename the file to use a .BLN file extension in Windows Explorer. 

 

Created April 25, 2016

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