Issue 56

Creating and Displaying Cross Sections in Surfer

The ability to slice a grid file in Surfer to create a file of data points along a specified line of section is a very tool powerful for our Surfer users. The ability to visually display the profile in Surfer, or combine profiles to display a cross section, is just as powerful.

When you slice a grid file, you have the option to create a BLN file or a DAT file. To get the data you need to display the results in Surfer, you want to choose the DAT file option. You then modify the resulting DAT file, convert it to a BLN file (it will be different than if you had saved the BLN file to begin with), and load it as a base map. If you have one slice (i.e., a topological profile), then you are done. If you have more than one slice (i.e., different surfaces at depth) you can load each BLN file as a base map, select all the base maps, and overlay them to create a cross section.

To start off, you must first have a grid file of your surface data and a BLN file defining the line of section. Then, you can follow the steps outlined below.

Step 1: Slicing the GRD files to create DAT files

1. Go to Grid | Slice.
2. Select the grid [.GRD] file you would like to create the cross section from and click Open.
3. Select the boundary [.BLN] file that contains the coordinates for the section line and click Open.
4. In the Grid Slice dialog box, click on the yellow open folder icon to the right of Output DAT File.
5. In the Save As dialog box, type in a file name and click Save.
6. Click OK and the DAT file is created.
7. Repeat for all the slices you want to create.

Use the Grid | Slice command to create a DAT file
containing data points along the line of section.

Step 2: Modifying the DAT files and converting them to BLN files

1. Open Surfer and go to File | Open.
2. Open the DAT files in the Surfer worksheet. For a cross section, you want to plot distance along section as the X variable (Column D in the DAT file) and elevation as the Y variable (Column C).
3. Highlight Columns A and B and go to Edit | Clear.
4. Highlight Column D and go to Edit | Cut (or press Ctrl+X).
5. Highlight Column A and go to Edit | Paste (or press Ctrl+V).
6. Highlight Column C and go to Edit | Cut (or press Ctrl+X).
7. Highlight Column B and go to Edit | Paste (or press Ctrl+V).

Open the DAT file in the Surfer worksheet, clear Columns A and B, and move the data
from Column D into Column A, and move the data from Column C into Column B.

Step 2a: If you want to simply show lines depicting the profiles without any fill, then follow these steps:

1. Scroll to the bottom of the file and note how many rows of data points you have. In this example, there are 101 rows of data.
2. Scroll back to the top and highlight row 1.
3. Go to Edit | Insert.
4. Type the number of data points in cell A1.
   
   
   

   Insert a row at the top of the file and enter
   the number of data points in cell A1.

5. Go to File | Save As and save it as a BLN file.
6. Repeat the above steps for all the DAT files you have.

Step 2b: If you want to fill the cross section with different fill patterns, then follow these steps:

1. Scroll to the bottom of the data file. In this example, there are 101 rows of data.
2. Highlight the last value in Column A (cell A101 in this example) and go to Edit | Copy (or press Ctrl+C).
3. Highlight the next blank cell in Column A (cell A102) and go to Edit | Paste (or press Ctrl+V).
4. In the first blank cell in Column B (cell B102), enter a value lower than the minimum Z value in all your data files. I will choose to enter -800 as I know it is lower than any other Z value.
5. On the next blank row (row 103), put in a 0 in Column A, and the minimum number entered in step 13 above (-800) in Column B.
6. Scroll to the top of the data file, highlight row 1, and go to Edit | Copy.
7. Scroll back to the bottom of the data file, highlight the next empty row (row 104), and go to Edit | Paste.
   
   
   

   Insert three additional rows of data to the bottom
   of the data file (rows 102-104 in this example).

8. Note how many rows of data points you have (104 rows of data now in this example).
9. Scroll back to the top of the file and highlight row 1.
10. Go to Edit | Insert.
11. Type the number of data points in cell A1.
    
    
    

    Insert a row at the top of the file and enter
    the number of data points in cell A1.

12. Go to File | Save As and save it as a BLN file.
13. Repeat the above steps for all the DAT files you have.

Step 3: Constructing the Cross Sectional Diagram

1. Load a BLN file as a base map by going to Map | Base Map, selecting one of the BLN files, and clicking Open.
2. Repeat for all BLN files you have.
3. Select all the maps with Edit | Select All and go to Map | Overlay Maps. If you just want to see the lines of the profile, skip to step 6.
4. Double click each Base map in the Object Manager, click on the Fill button, and set a specific fill for each map.
5. Drag and drop the Base maps in the Object Manager so that the lowest surface profile on the cross section is the highest in order in the Object Manager, and vice versa.
6. To change the scale of the map, double click on one of the Base maps in the Object Manager, go to the Scale tab, and set the scale you desire. You may want to uncheck Proportional XY Scalingto give the diagram some vertical exaggeration.

Load the BLN files as base maps, overlay them, and set the scale and
colors as you desire. You can choose to show the surface profiles as
lines (top) or fill them to create a solid looking cross section (bottom).