How To Quickly, Accurately and Easily Overlay a Georectified Image into Google Earth Using Global Mapper v9.0

Very Large Kingman Reef - Vector Shoreline View from Google Earth

This is the map that got me started on the mysterious very large Kingman Reef. The sides of the reef are depicted as 140-kms in length. Whereas Kingman Reef is actually a 1/10th of that size. Somebody misdigitized the reef, most probably in the early days of government produced vector maps. Oh, well, that's another story for another time. Meanwhile, let's talk about creating a nifty georectified image overlay and placing it into Google Earth (GE).

Using Global Mapper v9.0 (GM), the process to take an image, georectify it, export it as a KML/KMZ formated file and finally load it into GE is, as my title promises, quick, accurate and easy. How quick - about 2 to 5 minutes, depending on the complexity of the georectifying needed. How accurate - as accurate as you are able to georectify your image against known coordinates. How easy - even a caveman could do it. (I really do dislike that commercial, but it works here.)

Georectify Image

Step 1 - Georectifying an image using GM's process, lets you compare known coordinates (my previously constructed vector files of Kingman Reef) to my image (DigitalGlobe preview image composite of Kingman Reef). I typically create 3+ Ground Control Points (Affine). The GM windows allow for zooming to enable extremely precise georectifying of an image.

Georectified Image

Step 2 - Admire your work! If the image is whacked, you can go back into the georectifying process and fix it. I am an old pro at this, so my images typically line up just fine with my original vector files.

Export Georectified Image as KML/KMZ File

Step 3 - Select File option and Export Raster and Elevation Data. You are given a list of export options. Select Export KML/KMZ.

Format Your Image KML/KMZ File

Step 4 - My georectified image of Kingman Reef is small and is the only image loaded into my work area, so when it comes to KML/KMZ formatting options, I stick with default choices. If this were a very large image (many MBs), I would be able to grid it into manageable file sizes and load each one into GE. I use the KMZ file format. The zipped image and geocoding data take up much less space and load fast into GE.

Name and Save Your KML/KMZ File

Step 5 - Name your file and save it.

Kingman Reef - Landsat ETM+ Image from Google Earth

Double Click File and Enjoy Your Georectified Image in Google Earth

Step 6 - Now for the fun part. (Make sure you have GE loaded into your computer.) Double click your newly created Kingman Reef KMZ file, pause and then admire your work in GE. If you want to share your image overlay with the world, sign into GE and share away. If you just want to admire your handiwork, admire away!

Like I promised - using Global Mapper v9.0, the process to georectify, export and load an image into GE is quick, accurate and easy. Give it a try.

Enjoy!

Thoughts - DigitalGlobe, NGS & Kingman Reef

Kingman Reef - Landsat Image N-03-15_2000 (1-75,000)

Things can heat up at EVS Islands pretty fast, especially when National Geographic requests information about one of my mapping projects. Respected group that they are, they constantly research many areas prior to selecting a few primary areas for more thorough studies. One such area they are studying in depth is Kingman Reef. Since I have done mapping of the reef, one of their mapping team members contacted me and asked about my map of the reef. Needless to say, I was quite excited, yet apprehensive. I knew that the Landsat ETM+ imagery for this reef was not the most revealing. I remembered that in order to construct my EVS precision map I had to "trick" the image.

Kingman Reef - "Tricked" Landsat Image Over EVS Precision Marplot Map (1-75,000)

Using a Blend mode in Global Mapper that made the black colored sea transparent, the reef appeared as a murky yellow smudge. Using this yellow smudge to define the limits of the reef, I mapped it. Comparing my map to a nautical chart of the area, it turns out my EVS precision map of Kingman Reef is a solid effort. After numerous emails back and forth, I sent NGS my Kingman Reef vector files and various images to help them in their study of this reef.

Kingman Reef 10007409B01

Kingman Reef 10007409B01

Kingman Reef - Combined Image (10007318D01 and 10007409B01)

Let's talk about a "perfect world" where we all have access to the best imagery. I should have used DigitalGlobe's exquisite imagery of Kingman Reef to construct my map. A quick scan of DigitalGlobe's available imagery covering Kingman Reef reveals two nearly cloud-free views of the reef. An equally quick "cut and paste" gives me a revealing view of the reef. I could have made the ultimate map for this reef using these two images.

Let's do a "what if". What if my original Kingman Reef project had been constructed from these two DigitalGlobe images? What if I could have told the NGS rep that they were getting the best map availabe for this particular reef, because it was constructed from the best available imagery? What if I could have emailed them a copy of DigitalGlobe's imagery and my vector files for Kingman Reef? What if they would use and credit DigitalGlobe's imagery and my map of Kingman Reef in a future article? I think that is called "win-win".

And let's end this post with a proposition - DigitalGlobe, what would it take for you to make EVS Islands your island imagery charity case? Do you need me to be a non-profit? That is what I intend to do with EVS Islands. If you give me access to your island image archives, I promise I will make the best island maps possible. Using your imagery, I will teach young people the fine art of map making. I promise not to get in the way of your ongoing operations. I will quietly access island images from your archive, construct island mosaics and continue to make the best island maps possible.

Come on, DigitalGlobe, let's make a deal!