It is possible to get contour data from Google Earth and produce a contour map to develop a site’s landscape plan, regardless of size. However, employing a team of surveyors to create a very accurate base map is expensive. Alternatively, it is possible to extract 3D information from Google Earth and, using other software tools, make a contour map of the site with sufficient contour information to produce a concept design.
This movie shows how to extract 3D information from Google Earth, transform the data into a set of x,y and z coordinates, export data to Excel, create a contour map in QuikGrid, and export to gCADPlus.
The resolution of the satellite image limits the map’s accuracy, but valuable data can undoubtedly be obtained.
The figure below shows a base map developed from Google Earth data.
The following describes the steps taken to develop the site and contour map shown above using Google Earth data.
Step 1: Add a path to a Google Earth view
Open Google Earth, type the site’s address or KLM coordinates, and ‘fly’ to your destination. Here is an example: It is about 0.7 hectares in area.
Preliminary steps
Tip: We are going to ‘fly’ to the site and take the image, scale bar, and other data, so it is a good idea at this point to make sure that you have a top-down view. The keyboard shortcut “U” [without the quotes] is a convenient way to do this.
Use View > and make sure that the sidebar option is on.
Take off (do not show) the various layers in the tools at left so no text displays.
Turn off terrain views.
Save the image using the option on the top toolbar.
Create the contour information.
To create a contour map, you must use some Google Earth tools and add a path of points. The path will contain information on the x and y coordinates and an elevation (z value) of each point you add.
To create a path, select the Add Path option from the ‘Add’ drop-down menu > select the Add Path option. [The keyboard shortcuts are Control, Shift, and T.] The dialogue box below appears.
In the name box, type a suitable name for the path. It is a good idea to size the path dialogue box so that the display shows your entire site (and some extra) visible, ensuring that the path dialogue box is out of the way.
After adjusting the path colour and units [meters are used here], draw the path using the tabs in the dialogue box.
Tip: Do not close the path dialogue box before drawing the path with the mouse.
The figure below shows the result. A long path has been drawn, but yours may not need to be so long.
First, use File > Save My Places. Nothing appears to happen, but the path data is saved and visible in the box on the left.
Then, use File > Save Place As and save (export) the data as a kml file (not kmz). This file will contain the latitude, longitude, and elevation of each data point in the path, but some manipulation is needed to develop a contour map.
Close Google Earth.
Tips: Right-click in path mode to delete a point while working on a path.
To delete an existing path, in standard view, right-click and select Cut. Alternatively, delete the path from the Places dialogue box.
If it is a red ‘place’ icon, particularly one that showed up after typing in something in the search bar, click the’ X’ icon on the bottom right of the search box. While hovering over this ‘X’, it should say ‘Clear search results’. To activate the search bar, View> Select show sidebar, click the ‘X’ icon, then uncheck the sidebar option.
A key file is just the kml file zipped up – in other words, it is a compressed text file.
Step 2: Transform the Google Earth data into GPS form
We need to ‘normalise’ the data for contouring tool software. We must convert the kml file into x, y, and z coordinates.
We recommend using a free web resource called GPS Visualizer to do this.
Here is a link to the appropriate page in this resource – it is the home screen for GPS Visualizer:
https://www.gpsvisualizer.com/
The kml path file exported from Google Earth has been uploaded in this example. The output file will be a gpx file type associated with Garmin GPS devices.
Tip: Don’t forget to set the output format to GPX before you start the conversion process.
Save (download) your file (with the gpx extension)
Step 3: Add some 3D information to the gpx file
Again, we use a tool on the GPS Visualizer website to convert that data further. Here is the link:
https://www.gpsvisualizer.com/convert_input
The figure below shows a gpx data file being added. It is essential to set some output options carefully. Notably, the option comma-delimited needs to be checked and the add DTM data source option also set (we used ‘best available source’).
When that’s done, press the convert option. The figure below shows the result. Columns 2, 3, and 4 contain the information we need. In the next step, Excel will import the data and isolate the columns we want.
When complete, download the resultant csv file.
Step 4: Clean up data using Excel
The next step is to remove unwanted columns using Excel. Start Excel, open a new workbook > Data >Load CSV
Remove unwanted columns, leaving just latitude, longitude, and height. Save the data as another Space-Delimited Text file with the extension .txt and a meaningful file name. This is the data to use when importing into your contouring software.
Step 4: Generate a contour map
Here is an example using the free contouring application QuikGrid. We imported a mixed set of x,y, and z data.
Tip: It is sometimes easier to clean the data up in Excel, removing columns and hiding row 1. Then, copy the remaining contents to the clipboard (Ctrl-A) and paste them into a notebook page. Save the file as a txt file and use that file as an input to QuikGrid.
We export the grid and contour data to DXF, ready for gCADPlus import.
Step 5: Import the contour map to gCADPlus
Please open a new gCADPlus drawing (without using a template) and save it.
Place a screenshot of the Google Earth view of the site.
Using the File > Insert block, overlay the image with the contour information (it is in DXF format, so you must change the file type).
The figure below shows the result.
And here is the site with the grid turned off.
The gradient across the site is relatively shallow near the road and even shallower approaching the buildings.
The client is interested in planting wildlife corridors and establishing a wetland. We can now form some opinions about water drainage on the site and plan a suitable location for the wetland.
Here is an image showing the final design in the gCADPlus design environment.