Creating elevation contours within a house footprint from paper notes

Golden Software’s Surfer program can be used in so many applied-science industries for so many different uses, I sometimes forget that it is equally applicable to more business or art-oriented fields. I had a user contact me recently with the following request (paraphrased):

“I have a paper copy of the blueprint of a house, and on it I’ve written elevation measurements that I collected while surveying on the premises. I also have a DXF file of the floorplan of the house. How can I create elevation contours in Surfer and limit them to the shape of the house?”

What a neat application! From a piece of paper and one digital file, can Surfer generate a beautiful and informative contour map of elevation values? You bet it can!

There are a few steps to this process. You need to convert your paper data into digital x,y,z data, grid that x,y,z data, create a BLN file of the outline of the house, and blank the grid file with that outline. Then you can create a contour map of the blanked grid, and display the DXF of the floorplan overlaid on the contours if desired. The steps for each of these processes are detailed below, and sample files are attached so you can step through this process yourself.

1. Import the DXF as a base layer:
   1. Click Map | New | Base Map.
   2. In the Import dialog, select floorplan.dxf (vectorized using Surfer’s Draw menu commands from a JPG I found here) and click Open.
   3. In the DXF Import Options dialog, leave the defaults and click OK.
   4. Click on the Map in the Object Manager.
   5. On the Limits page in the Property Manager, make note of the xMin, xMax, yMin, and yMax.

6. Uncheck all four axes in the Object Manager.

2. Draw the boundary and export to BLN:
   1. Click Draw | Polygon.
   2. Click around the outside of your floorplan, holding the CTRL key while you click to snap the line to perfectly horizontal, perfectly vertical, or at a perfect 45 degree angle.
   3. Double click on the last point to finalize the polygon and then press ESC to exit drawing mode.

4. Uncheck the box next to the Base-floorplan.dxf layer in the Object Manager.
5. Click File | Export.
6. In the Export dialog, set the Save as type to BLN Golden Software Blanking (*.bln), give your file a name (like Blanking) and click Save.
7. On the Scaling page in the Export Options dialog, change the Scaling source to Map: Base-floorplan.dxf.
8. On the BLN Options page, in the Blank areas section, toggle Outside.
9. Click OK to export the BLN file.
10. If desired, uncheck or delete the Polygon from the Object Manager.

3. Digitize the data:
   1. Click File | Import.
   2. Select the PaperNotes.pdf file (a ‘scan’ of the paper notes you made in the field) and click Open.
   3. Right click on the Image in the Object Manager and click Order Objects | Move to Back.
   4. Check the box next to the Base-floorplan.dxf layer in the Object Manager.
   5. Click and drag the handles on the image until the image lines up with the DXF.
   6. Select the Base-floorplan.dxf layer.
   7. Click Map | Digitize.
   8. Click on the first point on the map where you have recorded an elevation value.
   9. In the Digitized Coordinates dialog, type a comma and a space after the second value in row 1 and then type your elevation value. In this example, the elevation value is displayed in red text next to the point on the image.

10. Click to the next empty row (2 this time).
11. Repeat steps 3h through 3j for the other elevation values you have recorded.
12. In the Digitized Coordinates dialog, click File | Save As.
13. In the Save As dialog, change the Save as type to Data Files (*.dat), give your file a name (like Elevation), and click Save.
14. Click X in the upper right corner of the Digitized Coordinates dialog to close it, and press ESC to exit digitizing mode.
15. If desired, you can now delete or turn off the Image.

4. Grid the digitized DAT:
   1. Click Grid | Data.
   2. In the Open Data dialog, select your Elevation.dat file and click Open.
   3. In the Grid Data dialog,
      1. Make sure the X, Y, and Z Data Columns are set to Columns A, B, and C from your digitized DAT file.
      2. Set your Gridding method (I’ll leave the default, Kriging).
      3. Make sure the Maximum in both the X Direction and Y Direction of the Grid Line Geometry section is larger than the maximums you made note of in 1e, and verify that the Minimums are less than the minimums you made note of. Since our minimums are in the low single digits and the maximums are around 850, using 0 for the minimums and 900 for the maximums here is just fine.
      4. If desired, increase the # of Nodes or decrease the Spacing to get a higher-resolution grid file (I will decrease the Spacing to 3 in both directions).
      5. Click OK.

4. Click OK in the dialog telling you the grid file was created.

5. Blank the grid file:
   1. Click Grid | Blank.
   2. In the Open Grid dialog, choose your Elevation.grd file and click Open.
   3. In the Open dialog, choose your Blanking.bln file and click Open.
   4. In the Save Grid As dialog, give your output file a name (like Elevation_blanked.grd) and click Save.
   5. Click OK in the dialog telling you the grid file was blanked.
6. Plot your contour map:
   1. Select your base map.
   2. Click Map | Add | Contour Layer.
   3. In the Open Grid dialog, select your Elevation_blanked.grd file and click Open.
   4. If prompted to expand the map limits, click No.

Now that your contour map is created, you can fill it as desired, and rearrange the layer ordering so the details in your floorplan display over top of the contours.

It’s amazing how much you can do from so little. From one piece of paper with some elevation values jotted down, you can create a stunning and informative image like this one!