EVS-Islands

Isla Pinta - Landsat N-15-00_2000 (1:90,000)

Isla Pinta - EVS Precision Marplot (1:90,000)

This project took about 4-hours to digitize. The shoreline is a composite of two images. The majority of the shoreline was taken from Landsat ETM+ imagery. When it is cloud free, this imagery is easy to work with. However, when you have cloud obscured shorelines, they are often impossible to discern. The second image used is DigitalGlobe imagery taken from Google Earth. This allowed me to digitize the eastern shore.

I have included four additional layers of information, besides the shoreline - a Vegetation Sparse layer, Land Bare, Land Lava and Land Rocky Shore. All of these layers were taken from the Landsat ETM+ image.

Isla Pinta - DigitalGlobe Image from Google Earth - Eastern Shore (Red Polyline)

I love DigitalGlobe imagery! It is the best to work with, but there are so many real and possible restrictions that apply to derivitive works, maps in particular, that it is more trouble than it is worth. The red polyline is what I digitized from the DG image. I imported it into Global Mapper and stitched it into my EVS precision shoreline.

Isla Pinta - EVS Precision Marplot with 50-meter Contours (1:90,000)

Isla Pinta - EVS Precision Marplot with 50-meter Contours 3D View (1:90,000)

I took my completed map image and georectified it on top of my Global Mapper data. I also added the SRTM data to create contours and explore 3D views of the island. The first map above has 50-meter contours. The second image is a 3D view of the island looking toward the NE.

Lonesome George at the Charles Darwin Research Station (Credit: Credit: Alison Llerena/CDRS)

And finally, here is Lonesome George. He is the last Pinta Island tortise. He was found in 1972 and removed to Santa Cruz Island. He has a couple of Wolf Island female tortises as his potential mates. So far Lonesome George continues to play hard to get. He is estimated to be between 80 to 90 years old. If he doesn't hook up with a female tortise soon his Pinta Island breed ends. I wish him well and his future mate many tortise children.

Enjoy!

Labels: DigitalGlobe, Ecuador, EVS Precision, Galapagos Islands, Google Earth, Landsat ETM+

Posted by Mr Minton at 1/04/2008 07:42:00 AM | Permalink | Comments | links to this post

Tuamotu Atoll LIIMs

List of Tuamotu Atoll LIIMs

What is a LIIM? It is an island image extracted from Landsat ETM+ imagery - Landsat Island Image Mosaic - LIIM. I have just completed LIIMs for the Tuamotu Atolls. These low-lying atolls are northeast of Tahiti and southwest of the Marquesas. I have created a total of 78 LIIMs - one for each atoll. They range in size (MBs) from Rangiroa Atoll at 28.7MBs to some of the small atolls under 1MB. As I did with the Greek and Turkish islands, each zipped file contains a JPG image and two georectifying files, they are 14.5 meters per pixel resolution and 300 DPI. I did not save them with DEM files as most of them are very low lying islands. All files are UTM projection with WGS-84 datum. A handful of the LIIMs have cloud-obscured areas, but overall the images are quite clear.

Before DigitalGlobe imagery in Google Earth, I did all of my island mapping with Landsat imagery. I would love to continue using DigitalGlobe imagery, but I feel the copyright restrictions are too cumbersome to deal with. Using Landsat imagery, one can map to their heart's content. One could even make money off of their mapping. Wouldn't that be a kick?

The same offer I made with my Greek and Turkish LIIMs applies to the Tuamotu Atoll LIIMs - drop me a line if you would like to try one of these out. I will email a link where you can download the appropriate LIIM. All I ask is that you give me some feedback as to their usefulness and ease of use. So, if you would like to try one of the Tuamotu Atoll LIIMs, drop me a line.

Enjoy!

Labels: DigitalGlobe, French Polynesia, Google Earth, Landsat ETM+, LIIM, Tuamotus

Posted by Mr Minton at 1/02/2008 11:25:00 PM | Permalink | Comments | links to this post

Three Vector Shoreline's Compared - WVS, SWBD and EVS Precision

One of my readers suggested I evaluate SWBD shorelines in comparison to other freely available shorelines. Previously, I compared these shorelines with my own EVS precision shoreline. I'll do it once more.

The WVS is widely available and manageable in size. There is another popular version of it called the GSHHS. It repairs varous WVS anamolies. In addition, it conveniently breaks the dataset into land, lakes, ponds and islands. At only 56MBs zipped, it is a very attractive option. As one can see in the two images, the WVS is the least precise of all large scale global shorelines. It is designed to be used at scales of 1:250,000 and above. For most of us designing projects for our classroom, employers or customers, this dataset does a fine job, it is free and the size is reasonable. It is when we need to do large scale precise shorelines that we require the next best global shorelines

Although the SWBD is a quality product and provides the end-user with precise SRTM water-defined shorelines, it tracks the water. The SWBD attempts to identify the place where the water meets the shore. That should be the shoreline, but it isn't. The top image shows the SWBD shoreline tracking the reef edges and ignoring the numerous motus within the reef. For us island mappers, the SWBD is not precise enough to identify the many shoreline features we require.

The same can be said for the NGA PGS shorelines. They are extremely precise, using Landsat ETM+ imagery as their base imagery. This is the same imagery I use to construct my EVS precision maps. I have the NGA PGS shoreline loaded into Marplot, a mapping package I use. The dataset is divided into 24 separate groups. My global coverage, using this dataset, is outstanding - except where clouds or other atmospherics obscure the shoreline or the shoreline consists of water-inundated areas (marsh, swamp, mudflats), which the NGA PGS product didn't identify. The cloud obscured areas on Landsat ETM+ imagery are validly poorly mappable to unmappable. The water-inundated areas are mappable, but the NGA contract called for the exclusion of these shoreline features, thus they were not mapped. I beg to differ. This is shoreline that must be mapped. There are massive river deltas NGA PGS mapped that depict shorelines that look nothing like the original Landsat ETM+ image, which is full of features that the NGA PGS product did not map. They just happen to be water-inundated. They are features you and I would describe as shoreline. Make no mistake, when the shoreline is cloud-free and not water-inundated, which most Landsat imaged shorelines are, this global shoreline dataset is outstanding. It's just all of those river delta islands that they didn't map that I have a problem with.

Four Vector Shoreline's Compared

However, my EVS precision shorelines are pretty outstanding as well. When one compares my hand-drawn shorelines to programmed color tracking shorelines (or many other automated processes), my hand-drawn shorelines track quite precisely. Something about using one's brain processing powers, manual dexterity and years of experience that consistently allows one to create more precise shorelines than the WVS, SWBD and NGA PGS products.

As I work with Landsat ETM+ imagery and learn more about the digitizing craft, I am certain software is available that could do what I do more accurately, faster and in much less time. But it wouldn't be as much fun! Would it?

Enjoy!

Labels: EVS, GSHHS, Landsat ETM+, NGA PGS, SRTM, SWBD, WVS

Posted by Mr Minton at 12/31/2007 09:30:00 AM | Permalink | Comments | links to this post