Breaklines
Breaklines are used when gridding to show discontinuity in the grid. A breakline is a three-dimensional boundary file that defines a line with X, Y, and Z values at each vertex. When the gridding algorithm sees a breakline, it calculates the Z value of the nearest point along the breakline, and uses that value in combination with nearby data points to calculate the grid node value. Surfer uses linear interpolation to determine the values between breakline vertices when gridding. Unlike faults, breaklines are not barriers to information flow, and the gridding algorithm can cross the breakline to use a point on the other side of the breakline. If a point lies on the breakline, the value of the breakline takes precedence over the point. Breakline applications include defining streamlines, ridges, and other breaks in the slope.
|
|
|
The gridding algorithm search uses a single Z value at the closest point along the line. The search can cross the breakline to search for data. |
Gridding algorithm searches use the specified anisotropy ratio when determining the distance to the breakline. The use of complex breaklines or a large number of breaklines slows the gridding process significantly. Breaklines cannot cross other breaklines or faults. Breaklines are not allowed with the No Search (use all of the data) search method for any gridding method.
The following gridding methods support breaklines:
- Inverse Distance to a Power
- Kriging
- Minimum Curvature
- Nearest Neighbor
- Radial Basis Function
- Moving Average
- Data Metrics
- Local Polynomial
Breakline Example
An example of a breakline .BLN format is:
|
|
|
A breakline file contains X, Y, and Z values in the .BLN file. |
Using Breaklines when Gridding
The breaklines options are displayed in the Breaklines section of the Grid Data dialog Options page when the selected interpolation method supports breaklines.
|
|
|
The Breaklines section is displayed when an interpolation method supports breaklines. |
Click the 
button in the File containing breaklines field to select the blanking file BLN containing the breaklines. In the Open dialog, specify the blanking file and click Open. The blanking file will be displayed in the File containing breaklines field. The number of traces and the number of total vertices are displayed under the file name. Delete the file name to exclude the breaklines from the interpolation process. Breaklines must contain 3 columns: X, Y, and Z. If the Z column is missing, the .BLN file cannot be used as a breakline.