EVS-Islands

Eiao Island - SRTM/DEM With Contours

Eiao Island - Contours 50-Meter Intervals

This was going to be a "How To" post, but I am not ready to tell you "How To" yet. I am still figuring all of the intricacies that apply to creating contours from Global Mapper. Needless to say, it is a fairly simple process. Load the SRTM DEM/HGT file, determine contour criteria, select "Create Contours" from the File Menu and you have created a series of contours.

Obviously, the contours are only as good as the underlying data (SRTM).  As I work more with the data and how it foots with Landsat and Google Earth 1-Meter Imagery, I will gain greater confidence in creating a new layer of information to be included with some of my high islands.

I think it could be a great addition to my EVS Islands. Just have to wait and see.

Enjoy!

Labels: atoll, EVS, Global Mapper, island, Landsat, map, Marplot, Marquesas, Pacific, Polynesia, SRTM

Posted by Mr Minton at 11/25/2006 12:32:00 PM | Permalink | Comments | links to this post

Reitoru Atoll (17˚50'S., 143˚06'W.), a low atoll, has no en-trance into the lagoon.

(SD Pub-126)

More information about Reitoru Atoll can be found at an interesting link that gives some facts about the very small population that makes a living from pearling.

This is the finished map with vectors taken from the Google Earth 1-meter resolution image. The map took about four hours to complete. It is a very solid effort.

Enjoy!

Labels: atoll, Digital Globe, EVS, France, Global Mapper, Google Earth, island, Landsat, map, Marplot, Pacific, Polynesia, Tuamotus

Posted by Mr Minton at 11/24/2006 10:05:00 AM | Permalink | Comments | links to this post

Landsat Image

Last night, I was searching for an island to work on. One not too large, but one I could finish in a single evening. I came across the above atoll. It is called Reitoru Atoll and is located in the Tuamotus. It looked like a great candidate.

As I do on all my projects, I searched various sources for more detailed imagery and Google Earth (GE) had it...cloud-free, 1-meter resolution of the atoll. I typically don't work in Google Earth to digitize, preferring Global Mapper (GM) instead. Before I can work off of this imagery, it must be loaded into GM and be georectified to ensure the vectors are created where they belong.

Image Rectification with 4 GCPs

Georectification uses an original image to apply the same lat/lon grid to a new image. Given enough Ground Control Points (GCP) applied to shared geographic features, the new image (GE image) can be easily laid on top of the original image (Landsat image). Upon loading a raster image in GM, you are asked if you would like to rectify the image or load it to view. Since I wanted to digitize from the new image, it was necessary to rectify it.

The actual process consists of five-steps for each GCP. Step-1: Select an outstanding feature identifiable on both images. Step-2: Zoom-in to clearly encompass the feature on both images. Step-3: Selet the feature location on the original image. This becomes the initial entry that will become the 1st GCPs lat/lon. Step-4: Select the same feature location on the new image. This is defined by its pixel location. It completes the entry for the 1st GCP. Step-5: Select "Add To GCP List", then move to the next GCP to georectify.

I use something called the Polynomial with 4+GCPs to georectify images. If an image needs to be tugged or pulled this method allows it. Ultimately, the images lay directly on top of each other - the new image on top of the original image. GM allows me to manipulate the new image to guarantee the best format from which to create my Enhanced Vector Shorelines (EVS).

Georectified Google Earth Image

Once the new image is georectified, I am able to create a very high quality product that I can then share with my readers. And that is how you georectify using GM. Isn't it easy?

Enjoy! And have a Happy Thanksgiving!

Labels: Digital Globe, georectify, Global Mapper, Google Earth, Landsat, map

Posted by Mr Minton at 11/21/2006 11:11:00 PM | Permalink | Comments | links to this post

Tehuata Atoll - Landsat Image S-07-15_2000 (1:15,625)

Tehuata Atoll - Marplot Map (1:15,625)

Tehuata Atoll aka Rekareka Atoll is small in comparison to it's neighbors. According to the UN Island Directory entry for Rekareka Atoll the island is uninhabited. Most probably the island is visited to harvest copra. The digitizing was fast and uncomplicated. GE has a 1-meter resolution image available for this island. I might use it later. I did a quick comparison and find that what I mapped is good.

Tehuata Atoll - Google Earth Image (1-15,125)

Tehuata Atoll - Marplot Map (1-15,125)

Okay, I am a perfectionist. I couldn't leave the map alone. Using the Google Earth 1-meter resolution imagery as base, I checked out my original vectors. A few minor adjustments. The primary change was a layer classification. I renamed EVS Land Gravel Sand, which I used once on Caldey Island UK, to EVS Land Distressed Sand. I believe that the grey sandy portion of the island is salt-water saturated. I like distressed sand instead of water saturated sand. Lots of things can distress sand besides water. And since it is my map, that is what I will continue to call it.

Enjoy!

Labels: atoll, Digital Globe, EVS, Global Mapper, Google Earth, island, Landsat, map, Marplot, Pacific, Polynesia, Tuamotus

Posted by Mr Minton at 11/20/2006 11:22:00 PM | Permalink | Comments | links to this post

If it wasn't for James Fee and his excellent work on Planet GS many GIS blogs would be read by the blog author and his or her close and loyal friends and family. Planet GS has allowed me to share my island projects with thousands of people throughout the world. I owe much of my blog's success to Planet GS.

My work is well received, being viewed by 50 to 100 visitors daily. My posts of island projects are typically found in the top five site references for a Google search. My point is - I am what I am (blog-wise) due to the quality of my work, the breath of my posts and the exposure offered by Planet GS.

So, it was with a great deal of displeasure I read the "Blogger Bashing" thread on James Fee's website dated November 02. To a person, everyone had fun bashing Blogger and the spamming-like problems that it supposedly creates in Planet GS.

As a Blogger blogger, I don't think the problem is with Blogger. The problem is with the blogger (little "b"). That is the individual blogging. Not all of us are HTML-pros. Not everyone works on the coding side of GIS. Some of us just have GIS-related ideas to share and Blogger is a great vehicle to carry our ideas forth. We sometimes screw up and post when we shouldn't post or post silly content. That is a problem of the blogger, not Blogger.

What am I trying to say? I resent that my site, EVS Islands, shows up on a list of Blogger derived sites (see the above link) as if it isn't worthy to be listed alongside non-Blogger sites. That is a bunch of elitist crap! I work long hours to ensure the quality of my posts meet my high exacting standards. I labor long and hard to maintain a consistently high standard of content. I never, knowingly, produce trite commentary, but strive to share topics relevant to my special interest, Enhanced Vector Shorelines of islands.

My product, high quality island maps, is for everyone, not merely the GIS expert. I am sure my readers include bored office workers, students and elderly dreamers. Great! And Blogger is how I am able to share my work.

James Fee - your work with Planet GS has allowed my product and that of others to be widely viewed throughout the world. If someone is messing up, determine the problem and let them know with a personal email. If they ignore your fair warning, since Planet GS is your site, delete their feed.

All of us in the GIS community truely appreciate Planet GS and all that you do.

Most especially this GIS Blogger blogger.

Labels: blog, Blogger, GIS, James Fee, Planet GS

Posted by Mr Minton at 11/20/2006 04:59:00 AM | Permalink | Comments | links to this post