Issue 62

Displaying Lake Bathymetry with Local Terrain Data Part 2

Part 1 of this article described how to grid and display lake bathymetry data in Surfer. There are many additional ways to display lake bathymetry data, including combining it with terrain data.

You can obtain a grid file of the local terrain (either grid data you have for the area, or download a DEM file from the internet), and display the local terrain with the lake as a flat surface or combine it with the bathymetry data to form a bowl shape. You can download a georeferenced aerial photo of the lake and place it behind the filled contours. Maps can be created in 2D or 3D, with multiple layer combinations. The variations are virtually endless.

This article details how to create some of these options:

1. Overlay Two 2D Contour Maps	4. Overlay Lake Contours w/Aerial Photo in 2D or 3D
2. Overlay Two 3D Surface Maps	5. Overlay 3D Terrain with a Flat Solid Lake Surface
3. Create a Seamless Grid	6. Overlay 3D Terrain with Flat Lake Contours

The bathymetric, terrain and aerial photo data used in this article was downloaded from the USGS Lake Tahoe Data Clearinghouse. The lake shoreline boundary was downloaded from the GIS Data Depot. You can download the exact files used in this article here.

All you need for these options is a grid file of the terrain data, a grid file of the bathymetric data, a BLN file defining the lake edge, and (only for option 3) a georeferenced aerial photograph.

One of the easiest ways to display lake bathymetry and terrain data together is to simply overlay two contour maps. To display contours of both the terrain and bathymetric data.

Follow these steps:

1. Blank the grid file of the lake bathymetry data outside the lake edge. If you have already done this, you can skip this step.
   1. Go to Grid | Blank.
   2. Select the grid file of the lake bathymetry data and click Open.
   3. Select the BLN file of the lake edge and click Open.
   4. Choose a location and name to save the blanked grid file to and click Save.
2. Go to Map | New | Contour Map.
3. Select the grid file of the terrain data and click Open.
4. Select the map and go to Map | Add | Contour Layer.
5. Select the grid file of the blanked bathymetric data and click Open. Both of the contour maps are created.
6. Double click on Map in the Object Manager to edit the properties of the map frame, such as scale or limits.
   1. Go to the Limits tab. Increase the Y minimum value and click Apply.
   2. Go to the Scale tab and reset the scale for the map and click OK.
7. You can double click on each of the Contours layer in the Object Manager to open the Contours Properties dialog and edit the individual properties for each layer, such as choosing fill and line colors and choosing to show a color scale.

Overlay contour layers of the lake bathymetry data and the terrain data for a composite map.

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One of the most effective ways to display lake bathymetry and terrain data together is to simply overlay two 3D surface maps.

Follow these steps:

1. Blank the grid file of the lake bathymetry data outside the lake edge. If you have already done this, you can skip this step.
   1. Go to Grid | Blank.
   2. Select the grid file of the lake bathymetry data and click Open.
   3. Select the BLN file of the lake edge and click Open.
   4. Choose a location and name to save the blanked grid file to and click Save.
2. Blank the terrain grid inside the lake edge. If you have already done this, you can skip this step.
   1. Go to File | Open.
   2. Select the BLN file and click Open. It will open in the Surfer worksheet.
   3. Change the value in cell B1 from a 0 to a 1, which indicates to blank inside the boundary.
   4. Go to File | Save As to save the changes as a new BLN file.
   5. Go to File | Close to close the BLN file.
   6. Go to Grid | Blank.
   7. Select the grid file of the terrain data and click Open.
   8. Select the BLN file saved in step d above and click Open.
   9. Specify a new name for the blanked grid file and click Save. The new blanked grid file will be created. This will show the terrain data with a “hole” where the lake is.
3. Next, determine if the lake data is based on depth (0 at the top with negative values for increasing depth) or if the lake data is based on true elevation. If the lake data is based on true elevation, then you can skip this step. If the lake data is based on depth, then we need to convert the Z values to true elevation.
   1. To convert the depth-based data to elevation-based data, we need to know the elevation of the lake surface. If you know this value, skip to step c. Otherwise, you may be able to find this by going to Map | New | Contour Map, selecting the unblanked terrain grid file and clicking Open.
   2. Move the cursor to the center of the lake area. The XYZ coordinates of the cursor location are displayed in the status bar at the bottom of the Surfer window. Note the Z value for the lake area. In this example, the elevation of the surface of the lake is 6229.045 feet. We need to add this value to the lake depth data.

       

      
      Move the cursor over the lake area in the
      contour map to view the Z value of the lake.
   3. Go to Grid | Math.
   4. Select the blanked grid file of the lake bathymetry data and click Open.
   5. In the Grid Math dialog, enter the function C = A+6229.045 (or enter your specific lake elevation).
   6. Click the yellow open folder icon if you wish in the Output Grid File C section to open the Save Grid As dialog. Specify a new grid file name and click Save.
   7. Click OK and the new grid based on lake elevation is created.
4. Go to Map | New | 3D Surface.
5. Select the blanked terrain grid file and click Open.
6. Select the map and go to Map | Add | 3D Surface Layer.
7. Select the blanked lake bathymetry grid file (based on elevation data) and click Open.
8. Double click on Map in the Object Manager.
   1. Go to the Scale tab.
   2. Set the scaling values to be what you want. For example, you may want to minimize the vertical exaggeration by decreasing the Length value for the Z Scale.
   3. Click OK.
9. Double click on one of the 3D Surface layers in the Object Manager.
   1. On the General tab, click on the Upper button in the Material Color section.
   2. Set the Colormap to show the colors you desire.
   3. Click OK and OK.
   4. Repeat for the other 3D Surface layer.

Overlay 3D surface layers of the terrain and lake data for a composite map.

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One of the most effective ways to display lake bathymetry and terrain data together is as a 3D surface map. Although the process starts the same as option 2 above, this method is different in that a single grid file and a single surface map is created instead of two. This might be useful if you want to use a continuous color scale between the terrain and lake data, or if you want to perform other grid functions on the entire data set.

Follow these steps:

1. Blank the grid file of the lake bathymetry data outside the lake edge. If you have already done this, you can skip this step.
   1. Go to Grid | Blank.
   2. Select the grid file of the lake bathymetry data and click Open.
   3. Select the BLN file of the lake edge and click Open.
   4. Choose a location and name to save the blanked grid file to and click Save.
2. Blank the terrain grid inside the lake edge. If you have already done this, you can skip this step.
   1. Go to File | Open.
   2. Select the BLN file and click Open. It will open in the Surfer worksheet.
   3. Change the value in cell B1 from a 0 to a 1, which indicates to blank inside the boundary.
   4. Go to File | Save As to save the changes as a new BLN file.
   5. Go to File | Close to close the BLN file.
   6. Go to Grid | Blank.
   7. Select the grid file of the terrain data and click Open.
   8. Select the BLN file saved in step d above and click Open.
   9. Specify a new name for the blanked grid file and click Save. The new blanked grid file will be created. This will show the terrain data with a “hole” where the lake is located.
3. Next, determine if the lake data is based on depth (0 at the top with negative values for increasing depth) or if the lake data is based on true elevation. If the lake data is based on true elevation, then you can skip this step. If the lake data is based on depth, then we need to convert the Z values to true elevation.
   1. To convert the depth-based data to elevation-based data, we need to know the elevation of the lake surface. If you know this value, skip to step c. Otherwise, you may be able to find this by going to Map | New | Contour Map, selecting the unblanked terrain grid file and clicking Open.
   2. Move the cursor to the center of the lake area. The XYZ coordinates of the cursor location are displayed in the status bar at the bottom of the Surfer window. Note the Z value for the lake area. In this example, the elevation of the surface of the lake is 6229.045 feet. We need to add this value to the lake depth data.

       

      
      Move the cursor over the lake area in the
      contourmap to view the Z value of the lake.
   3. Go to Grid | Math.
   4. Select the blanked grid file of the lake bathymetry data and click Open.
   5. In the Grid Math dialog, enter the function C = A+6229.045 (or enter your specific lake elevation).
   6. Click the yellow open folder icon, if you wish, in the Output Grid File section to open the Save Grid As dialog. Specify a new grid file name and click Save.
   7. Click OK and the new grid based on lake elevation is created.
4. Now we can mosaic the grids to create a single grid. Go to Grid | Mosaic.
5. Select the blanked terrain grid file, and click Open.
6. In the Grid Mosaic dialog, click the Add button.
7. Select the blanked lake bathymetry grid file (based on elevation data) and click Open.
8. Click the yellow open folder icon, if you wish, in the Output Grid File section to open the Save Grid As dialog. Specify a new grid file name and click Save.
9. Click OK to create the mosaicked grid file.
10. Go to Map | New | 3D Surface.
11. Select the mosaicked grid file and click Open. The surface map is created.
12. Double click on Map in the Object Manager.
    1. Go to the Scale tab.
    2. Set the scaling values to be what you want. For example, you may want to minimize the vertical exaggeration by decreasing the Length value for the Z Scale.
    3. Click OK.
13. Double click on the 3D Surface layer in the Object Manager.
    1. On the General tab, click on the Upper button in the Material Color section.
    2. Set the Colormap to show the colors you desire.
    3. Click OK and OK.

Mosaic the terrain and lake grid files to create a single grid file for the entire region.
Use this single grid file to create one continuous map, or in other grid functions.

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You can give the map a real-world appearance by adding a georeferenced aerial photo to the lake bathymetry data. You can display the map in 2D, or add a 3D surface layer to display it in 3D.

Follow these steps:

1. Blank the grid file of the lake bathymetry data outside the lake edge. If you have already done this, you can skip this step.
   1. Go to Grid | Blank.
   2. Select the grid file of the lake bathymetry data and click Open.
   3. Select the BLN file of the lake edge and click Open.
   4. Choose a location and name to save the blanked grid file to and click Save.
2. Go to Map | New | Contour Map.
3. Select the blanked grid file of the bathymetry data and click Open.
4. Select the contour map and go to Map | Add | Base Layer.
5. Select the georeferenced image file and click Open.
6. In the Object Manager, drag the Base layer so that it is under the Contours layer.
7. Double click the Contours layer and set the contour roperties that you wish.

    

   
   Add a georeferenced aerial photo to a contour map
   of the blanked bathymetry data.
8. To add a 3D aspect to the map, you can add a 3D surface layer. Select the map and go to Map | Add | 3D Surface Layer.
9. Select the grid file of the local terrain and click Open. A 3D surface layer is added to the map.
10. Double click on Map in the Object Manager.
    1. Go to the View tab, and set the Rotation and Tilt values to be what you desire (45° and 30° are the default values, respectively).
    2. Change the Projection to be Perspective.
    3. Click Apply.
    4. Go to the Scale tab.
    5. Set the scaling values to be what you want. For example, you may want to minimize the vertical exaggeration by decreasing the Length value for the Z Scale.
    6. Click OK.
11. Double click on the 3D Surface layer in the Object Manager.
    1. Go to the Overlays tab.
    2. Change the Color Modulation to be User overlay color only.
    3. Click OK.

Add a georeferenced aerial photo and a contour map of the blanked
bathymetry data to a 3D surface map for a real-life 3D view.

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You can download or grid local terrain data to display around the lake. In many cases, the data for the lake area is a flat surface in the grid file. When this is the case, it is very easy to change the color of the flat lake surface to a single blue color to more effectively represent water, instead of using one of the gradient colors of the surrounding terrain.

Follow these steps:

1. Blank the grid file of the terrain data outside the lake edge. If you have already done this, you can skip this step.
   1. Go to Grid | Blank.
   2. Select the grid file of the terrain data and click Open.
   3. Select the BLN file of the lake edge and click Open.
   4. Choose a location and name to save the blanked grid file to and click Save. This is a grid file only of the flat lake surface, with all the surrounding terrain data blanked.
2. Then we will reverse the process and blank the terrain grid inside the lake edge. If you have already done this, you can skip this step.
   1. Go to File | Open.
   2. Select the BLN file and click Open. It will open in the Surfer worksheet.
   3. Change the value in cell B1 from a 0 to a 1, which indicates to blank inside the boundary.
   4. Go to File | Save As to save the changes as a new BLN file.
   5. Go to File | Close to close the BLN file.
   6. Go to Grid | Blank.
   7. Select the grid file of the terrain data and click Open.
   8. Select the BLN file saved in step d above and click Open.
   9. Specify a new name for the blanked grid file and click Save. The new blanked grid file will be created. This will show the terrain data with a “hole” where the lake is located.
3. Go to Map | New | 3D Surface.
4. Select the flat lake-only grid file created in Step 1 above and click Open.
5. Select the map and go to Map | Add | 3D Surface Layer.
6. Select the terrain-only grid file created in Step 2 above and click Open. The two maps are overlaid.
7. Double click on Map in the Object Manager.
   1. Go to the Scale tab.
   2. Set the scaling values to be what you want. For example, you may want to minimize the vertical exaggeration by decreasing the Length value for the Z Scale.
   3. Click OK.
8. In the Object Manager, double click on the 3D Surface layer created from the terrain-only grid file.
   1. On the General tab, click on the Upper button in the Material Color section.
   2. Set the Colormap to show the colors you desire.
   3. Click OK and OK.
9. In the Object Manager, double click on the 3D Surface layer created from the lake-only grid file.
   1. On the General tab, click on the Upper button in the Material Color section.
   2. In the Colormap dialog, select the color node on the left, and select a blue color from the Color drop-down menu.
   3. Select the color node on the right, and select the same blue color from the Color drop-down menu.
   4. Select any intermediate color nodes and press the Delete key on the keyboard to delete them.
   5. Click OK and OK.

Fill the surface map of the lake with a solid color to better represent the water surface.

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You can download or grid local terrain data to display around the lake. In many cases, the data for the lake area is a flat surface in the grid file. When this is the case, you can display a contour map over the flat lake surface to show the bathymetry data.

Follow these steps:

1. Blank the grid file of the lake bathymetry data outside the lake edge. If you have already done this, you can skip this step.
   1. Go to Grid | Blank.
   2. Select the grid file of the lake bathymetry data and click Open.
   3. Select the BLN file of the lake edge and click Open.
   4. Choose a location and name to save the blanked grid file to and click Save. This will be used to create the contours.
2. Blank the grid file of the terrain data outside the lake edge. If you have already done this, you can skip this step.
   1. Go to Grid | Blank.
   2. Select the grid file of the terrain data and click Open.
   3. Select the BLN file of the lake edge and click Open.
   4. Choose a location and name to save the blanked grid file to and click Save. This is a grid file only of the flat lake surface, with all the surrounding terrain data blanked.
3. Then blank the terrain grid inside the lake edge. If you have already done this, you can skip this step.
   1. Go to File | Open.
   2. Select the BLN file and click Open. It will open in the Surfer worksheet.
   3. Change the value in cell B1 from a 0 to a 1, which indicates to blank inside the boundary.
   4. Go to File | Save As to save the changes as a new BLN file.
   5. Go to File | Close to close the BLN file.
   6. Go to Grid | Blank.
   7. Select the grid file of the terrain data and click Open.
   8. Select the BLN file saved in step d above and click Open.
   9. Specify a new name for the blanked grid file and click Save. The new blanked grid file will be created. This will show the terrain data with a “hole” where the lake is located.
4. Go to Map | New | 3D Surface.
5. Select the flat lake-only grid file, created in Step 2 above, and click Open.
6. Select the map and go to Map | Add | 3D Surface Layer.
7. Select the terrain-only grid file, created in Step 3 above, and click Open. The two maps are overlaid.
8. Double click on Map in the Object Manager.
   1. Go to the Scale tab.
   2. Set the scaling values to be what you want. For example, you may want to minimize the vertical exaggeration by decreasing the Length value for the Z Scale.
   3. Click OK and OK.
9. In the Object Manager, double click on the 3D Surface layer created from the terrain-only grid file.
   1. On the General tab, click on the Upper button in the Material Color section.
   2. Set the Colormap to show the colors you desire.
   3. Click OK and OK.
10. In the Object Manager, double click on the 3D Surface layer created from the lake-only grid file.
    1. On the General tab, click on the Upper button in the Material Color section.
    2. In the Colormap dialog, select the color node on the left, and select white from the Color drop down menu.
    3. Select the color node on the right, and select white from the Color drop-down menu.
    4. Select any intermediate color nodes and press the Delete key on the keyboard to delete them.
    5. Click OK and OK.

     

    
    Fill the surface map of the lake with a solid white color
    if you want to see contours on top of the surface.
11. To add the contours, select the map and go to Map | Add | Contour Layer.
12. Select the grid file of the bathymetry data that is blanked outside the lake edge, created in Step 1, and click Open.
13. Double click on the contour map to edit the properties. You can choose to fill the contours, or change the line and fill properties.
14. Click OK.

A contour layer of the lake bathymetry only is added to the 3D surface layers. The contour lines were
set to a color gradient, and the contour levels were filled with the same color gradient.