HOW TO: Move a Topomap from the Sunmap DVD into Google Earth (on a Mac)
The goal-state: viewing your topomap on Google Earth, so you can overlay it with your GPS trails.
Note: This document is really just a reminder for me on how to do this, because it’s unreasonably tricky for something that should be be very easy.
Before you get started, you need the SunMap Digital Maps DVD. This contains (amongst other things) scanned images of all of the 1:25K topomaps for Queensland – 483 of them. And unless you have Photoshop, you need to be able to run Windows on a Virtual Machine (VM) on your Mac. I’m using Parallels for Mac this week.
You don’t need to use the viewing software that comes with the DVD, because all of the maps are stored as files on the DVD and can be pulled off through the Finder. But the software does allow you to see what parts of Queensland are covered by maps, and where the individual map boundaries are.
I had problems running the viewing software on my Mac. It’s Windows only, so I needed to run it via a Windows VM. But for some reason it wouldn’t run from my USB-mounted SuperDrive. To resolve this, I burned an image of the DVD and mounted that image on my Mac via Disk Utility. I then browsed to that folder on my Windows VM and ran the “setup.exe” found on Disk 1. This approach worked fine.
Before you begin: Mounting the Sunmaps DVD from a Disk Image
I prefer to use a local copy of the DVD on my hard drive, rather than putting the DVD into the drive each time. It’s faster, I can have both DVDs mounted at once, it means I’ve got a backup copy of the DVD, and it means I can actually run the DVD software (as mentioned above).
There are a number of ways to burn an ISO DVD image – I used the “dd” command from the Terminal – once for each DVD. Each copy took about 40 mins to create.
$dd if=/dev/disk1 of=sunmap-dvd1.iso
You can then mount this ISO file as a drive by using “File-Open” from Disk Utility and browsing to the folder where you saved your “sunmap-dvd1.iso” image.
Extracting a TopoMap from the Sunmaps DVD
Use the Sunmaps Digital Maps viewer software to move around the Queensland area and find the name of the map you are after. It will be displayed in the bottom right-hand corner of the screen.
Once you know the name of the map you want, here are the steps to getting it into Google Earth as an overlay, so you can look at a in 3D, with GPS trails displayed.
Step 1. Find the map file on the DVD.
The files are named something like “9541-13 Springbrook.evw” and are about 10Mb big.
The names of these files (eg. “9541-13 Springbrook”) are what you see on the front of the paper map:
Step 2. Convert the file from ECW format to TIF.
The ECW format can’t be recognised by Google Earth, nor any of the affordable Mac graphics apps. So I used the Windows app IrfanView to convert it to a TIF file (this is why you need to be able to run Windows on your Mac). Note that if you use IrfanView, you’ll also need to install the plug-ins in order to open the ECW files.
Once you’ve installed IrfanView on your VM, you can just double-click the file on your Mac and it will open in IrfanView on your VM. The ECW file is actually a full image of the topomap, including the borders, so we need to crop it.
In IrfanView, you can use a “Custom Crop” which is handy to preselect about the right portion of the map. Do this via “Edit-Create Custom Crop Selection… (Shift C)”.
I start with these settings, click “Save and Apply”, and then tweak the crop lines manually by zooming in on the corners. Note that these maps are always slightly skewed so you have to check each corner to ensure you don’t select any of the map border.
Once you’re happy with the cropped image containing only the topomap, save it in uncompressed TIF format (about 80Mb) to somewhere on your Mac. I also include the year of the map (found on the map cover). So in this case I’d name it “9541-13 Springbrook 1998.tif”
Step 3. Import the TIF file into Google Earth as an Image Overlay
Fire up Google Earth. Zoom roughly to the area where this map is going to sit. It is useful to turn off the “Tilt when Zoom” setting in Google Earth temporarily.
Use “Add-Image Overlay” and add a link to the TIF file created above. Google Earth will display the map, but not at the correct location nor the correct size.
To place the overlay in the correct location, look at the original map image (the ECW you opened in IrfanView) and find the corner coordinates for the top left and bottom right corners.
Enter these into the “Location” tab of the overlay. Reduce the opaqueness of the image to 50% so you can see how well features like lakes and roads match up. Use the Worldwide UTM 1km gridlines to precisely lineup the map onto the terrain (although sometimes these are in the wrong place on the map!) The scanned map might need a little rotation – it’s easiest to do this by changing the value in the “Location” section and tabbing to the next field so it takes effect.
And we’re done! Now you can zoom in and use it to plan your next trip.
Next topic? How to get that topomap onto your Garmin eTrek GPS!
After that? How to get that topomap onto “BitMap” on your iPhone, so you can use your iPhone as a GPS device without cellular network coverage.