Contour data from Google Earth

A contour map is a valuable aid in developing a conceptual landscape plan for a site, no matter what the size. It is expensive to employ a team of surveyors to produce what will be a very accurate base map. As an alternative, it is possible to extract 3D information from Google Earth and, using other software tools, make a contour map of the site.

YouTube movie  This movie show step by step 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 accuracy of the map is of course limited by the resolution of the satellite image, but useful data can certainly be obtained.

The figure below shows a base map developed from Google Earth data.

A description of the steps taken when developing the site and contour map shown above using Google Earth data follows.

Step 1:  Add a path to a Google Earth view

Open Google Earth, type the address or KLM coordinates of the site, and ‘fly’ to your destination. Here is an example. It is a site that’s about 0.7 hectares in area.

To create a contour map, it is necessary to use 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, from the ‘Add’ drop-down menu > select the Add Path option. The dialog box shown below appears.

Type a suitable name for the path in the name box. It is a good idea to size the path dialog box so the display shows your entire site (and some extra) visible with the path dialog box out of the way.

After adjusting the path color and units using the tabs in the dialog box, draw the path. The figure below shows the result. Quite a long path has been drawn. 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 at 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 it needs some manipulation in order to develop a contour map.

Close Google Earth.

Tips: To delete a point while working on a path, right-click while in path mode.

To delete an existing path, in normal view, right-click and select Cut.

If it is a red ‘place’ icon, particularly one that showed up after typing in something in the search bar, on the bottom right of what is apparently the search box click the ‘X’ icon. 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 kmz file is just the kml file zipped up.

Step 2: Transform the Google Earth data into GPS form

We need to ‘normalize’ the data so it can be used in contouring tool software. Put simply, we need to 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/

In this example, the kml path file exported from Google Earth has been uploaded and the output file will be a gpx file type that’s associated with Garmin GPS devices.

Save 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 web site. Here is the link:

https://www.gpsvisualizer.com/convert_input

The figure below shows a gpx data file being added. It is important to carefully set some output options. Notably, the option comma-delimited needs to be checked and add DTM data also set.

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 be used to import the data and isolate just 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 and using a meaningful file name, save the data as another csv file. This is the data to use when importing into your contouring software.

Step4: Generate a contour map

Here is an example using a free contouring application QuikGrid. We simply imported a mixed set of x,y,z data.

 

We export the grid and contour data to DXF ready for gCADPlus import.

Step5: Import contour map to gCADPlus

Open a new gCADPlus drawing (without using a template) and save it.

Place a screenshot of the Google Earth view of the site.

Using File > Insert block overlay the image with the contour information.

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 becomes 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.