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Mapping an arboretum using Google Earth
It is possible to combine Google Earth images with CAD software and store lots of non-graphic information about species planted on a farm or in (say) an arboretum - a collection of species growing under natural rainfall conditions. In this paper, we describe the methodology used to capture images from Google Earth that cover the site of an arboretum and incorporating them into an accurate CAD drawing. Once that's done, it is possible to gain all sorts of information not available from a Google map image - calculate areas, provide detailed design, show time course data, add and edit attributes etc..
Start Google Earth and zoom in on an area of interest using the + and - slider to the right of the Google Earth screen. In this example, we focus on an arboretum. The figure below shows an arboretum at the Waite Institute in Netherby, South Australia. The arboretum is located above and below the curving roadway shown in the image below.
Take a screen snapshot ('dump') to the Windows or Apple clipboard (using the PrntSc key in Windows or the Command Shift 3 combination in the Apple Mac).
Tip: Before taking each screen grab, use the U key on the keyboard to get a top down view and the N on the keyboard to orient the image to the north
The image below has been taken at the maximum useable magnification of the Google Earth view. Any higher zoom factor leads to pixilation and loss of resolution.
Tip: As an alternative to the screen capture methods described above, a screen capture program such as the one built in to Windows 7 or SnagIt from TechSmith could be used. Clearly, the higher the resolution on the screen, the better the result.
In Google Earth, it is also possible to turn on a grid as shown (faintly) in the image below. The latitude and longitude of one intersection point on the grid is also available for display, as are GPS values of points (say the location of trees). Write these latitude and longitude values down as they will help register the image in your CAD software at a later stage.
Tip: Make sure that a scale shows in the bottom left of the Google Earth image when you capture an image.
After performing a screen grab, you might then want to use your image editor to crop the image.Tip: If you do use an image editor to crop several images, make each image a standard size so they can be stitched together.
By switching to Google maps from Google Earth it is also possible to plot the street network and the names of roads on the image. We suggest that you do that and save it as a separate image.
If you need extra high resolution, it is possible to use the Google Earth tool to zoom in and take screen grabs of several overlapping areas of interest (overlap by about 25%) and use image stitching software such as AutoPanoGiga or PtGui to stitch the images together. The figure below shows one step in a magnification and stitching process.
The image below has been cropped in an image editor. This is one of the images we will work with in our CAD software.Tip: If you use image stitching software, you will need to add the Google copyright notice back in place as the stitching process may remove it..
You might also want to use your image editing software to save a copy of the image above with reduced contrast.
Now start your CAD software. Make a new layer for your background image and insert the raster image into it and a new layer for a CAD symbol(s) that will be placed on top of the Google Earth image.Tip: Make sure that you have set the layer order (stacking) correctly otherwise your CAD symbol may disappear behind the image.
Scale the image by zooming in on Google's scale and, using GardenCAD's distance (measure) command to check on distance reported. In our example, the Google scale value was 42 feet read and read as 1.898 meters using the distance tool in the CAD software. Converting 42 feet to meters gives a value of 12.8 meters, so we need to scale the image by 12.8/1.898 = 6.464. This is done by selecting the image, right clicking and choosing the SCALE command.Tip: You may be able to see from the screen grab here that we are using GardenCAD in the Apple environment. GardenCAD works well on the Mac.
Now it is just a matter of making a new layer and inserting symbols above the location of the plant. In the example below, we have used just one GardenCAD symbol and used the Edit Attribute tool to pop up the stored attributes (non text information) for the individual plant at that location.
Now, when we need to determine the name and location of a plant, it is a simple job, just double click on the symbol. The figure below shows an example:
I have chosen a light weight symbol to represent one of the species in the arboretum, but any of GardenCAD's symbols could have been used. In fact, if the arboretum contained less than 90 trees, a separate symbol could be used for each species.
All GardenCAD symbols have in-built attributes that can be used to store non-graphic information about the particular species (see below). Although not all text associated with a particular attribute is visible and shown here, it is able to be read quite easily by the user, simply by double clicking on the symbol and reading text information in the Properties box.
Other information that could be stored in these attributes might be the GPS coordinates of the tree so that anyone interested in that species could be directed to it using their personal GPS navigator. That information about GPS coordinates can be gained from Google and then further refined in a 'ground truthing' operation.
More advanced users could create their own species indicator and store large quantities lots of attribute information - sampling time, leaf condition, pests observed, leaf analysis etc.
Google Earth stores satellite information at each pass. The figure below shows a time series example taken from a farm in Argentina. The series ranges from 2002 to 2009 and it is possible to see the rapid growth of some species.
It is worth using a sophisticated image editing program like Photoshop to sharpen and improve the colour balance of these images.
Here is an image taken from the Sept 2009 photograph after some 'photoshopping' - sharpening and colour balancing.
It is well worth looking at these time course images, as not only does the quality of photographs taken at different time vary but, because Google Earth images are taken at different times of the year, reflectivity of some species varies as shown above. Deciduous trees (Oaks or Willows?) lining a roadway are in early leaf and show as light coloured images.
In the three years between the image above and the one below, considerable growth has taken place in the arboretum.
The 2009 image had the best quality so this was used inside CAD software as the base plan.
The Google scale value was 95 meters and read as 274.6 units (meters) using the distance tool in the CAD software, so we need to scale the image down by 95/274.6 = 0.345
Here is a close up of the registration of the image in the CAD software. Distance measurement in the CAD software now closely aligns to that of Google Earth.
A special symbol was developed by this users for capturing and detailing much information about individual plants - year planted, botanical and common names, GPS coordinates and flowering time. Other attributes such as fertilizer application etc. could be added. The density of hatching of the symbol was set so that the underlying Google Earth image could still be seen under the symbol.
Here we have saved data about the location and flowering time of the Rusty Kurrajong, Brachychiton bidwilli
We have given this species a user code (unique identifier) of 067. This was used to create a GardenCAD page dealing with cultivation notes and other observations about this particular species. The image below shows a GardenCAD page (named 067) set up with information about the species.
As more accurate information about the site becomes available, that can be added on top of the Google Earth image. The accurate CAD layout for the kitchen gardens area is shown below.
Once accurate vector information has been added, calculations such as area can be made from the CAD data. The figure below shows an area calculation being made.
It will be interesting to see how the hybrid CAD and Google Earth data develops over the life span of the arboretum.
Mapping larger stands of vegetation
It is possible to draw polylines around larger stands of vegetation and add single symbols to carry information about number of trees planted, year planted and botanical names.
Here is a link to a YouTube movie that discusses this issue.
Detailed arboretum work