EVS-Islands

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!

Labels: DigitalGlobe, georectify, Global Mapper, Google Earth, Kingman Reef, KML, KMZ

Posted by Mr Minton at 2/28/2008 06:20:00 AM | Permalink | Comments | links to this post

I am not a programmer. I muddle my way through HTML and have a rudimentary idea on how KML files are structured. Much of my mapping consists of polylines that ultimately make up a shoreline or a polygon that encloses an EVS layer of information. I construct most of my polylines within Global Mapper (GM) using it's digitizing capabilities. Quite often I find myself digitizing from within Googe Earth (GE). I have constructed polyline files consisting of 20,000 vertices from within GE. My files are ultimately saved in KML format and deposited onto my desktop. I am going to share my "poor man's work around" using MS Word. As the title indicates, I will explain one way to quickly and easily convert KML map files into Arc/Info Ungenerate format. My process is fast and Arc/Info Ungenerate format easily drops into any number of mapping programs.

KML File Loaded into MS Word

A KML file will load directly into MS Word. The format is what you see in the above image. Once loaded you can begin modifying it.

Delete Heading To First Lon-Lat

KML layout for vertices is lon,lat,elevation(sp). But I'm ahead of myself. You must first delete the KML heading. You will not need it for an Arc/Info Ungenerate format.

Add Polyline ID #

At the line directly above the first lon add the number 1. Each unique polyline is identified with a number and END at the end of each polyline/polygon or END END at the very end of a file.

Find and Replace

Now we get fancy. When digitizing within GE make sure you digitize directly at ground level. That will zero out the elevation. Each set of vertices includes a "0, ". Within MS Word I "Find" "0, " and "Replace" it with a manual line break "^|". Position the cursor at the beginning of the file and select "Replace All".

Conversion is Almost Complete

This file consists of 1,008 vertices and took a second to process. If my memory serves me right, the 20,000 vertice file took about five seconds to convert. This process is very fast.

Delete Bottom KML Script

At the end of the list of vertices, delete any remaining KML script.

END END and Save as a Text File

Since this is a single polyline, enter a double END END to end the file. And there you have a properly formatted Arc/Info Ungenerate file. Save it as a WhatEver.txt file and it is ready to load into your favorite mapping program

Import Modified File Into Global Mapper

I work primarily with two mapping programs. First, I'll walk you through an import into Global Mapper. This is its initial screen. Select file and determine the type of format your target file is in - .txt.

Select The File

Browse and select your file.

Adjust Settings as Needed

Global Mapper recognizes your selected file type and any potential settings. If you need to modify any of them, this is the screen where you would do that. I want my polyline to show up as an EVS Shoreline. Once everything looks alright, select "OK"...

And There It Is, One Modified GE KML File That is Now an Arc/Info Ungenerate File!

Importing The Modified File Into Marplot

Marplot, an excellent mapping freeware package, is my second mapping package. It is where I maintain my extensive database of islands and other layers of information. Go to File and Import.

Select The Modified File To Import

Browse and select the file to import.

Select "No" At This Prompt

Since the file is not a native Marplot map file, select the "NO" option here.

And There You Have It!

Within Marplot the file will load into the layer that happens to be at the top of your layer list. I always keep my Temporary layer at the top within Marplot. After I have ensured that my imported file looks fine, I move it to it's appropriate layer.

And that's how you convert a KML map file into an Arc/Info Ungenerate map file. Cool, huh?

Enjoy!

Labels: Global Mapper, Google Earth, KML, Marplot, MS Word, Ungenerate

Posted by Mr Minton at 5/30/2007 02:35:00 PM | Permalink | Comments | links to this post