EVS-Islands

PGS (Red) vs EVS (Orange) - Landsat Image Detail (Enderbury Island Kr)

The above image is from a Landsat ETM+ 2000 image (S-02-00_2000) that was used in the development of the NGA Prototype Global Shoreline (PGS) (see previous post for link). Since I previously digitized this island, I used it to compare my vectors (EVS) to the newly released NGA vectors (PGS). The image retains the pixel shapes (little squares) that EarthSat used in creating the PGS. The PGS is the "red" line. My EVS is the "orange" line. This island is a very simple shoreline that was easy to digitize. It appears that the PGS vectors are nearly complete for the island. They did not create vectors for the southern end of the island that had minor cloud obscuration. I did create vectors to cover that area using other sources, WVS, internet maps of the island, etc.

PGS vs EVS - Detail (Enderbury Island KR) Anti-Alias Pixel Effect

The above image is identical to the previous image, but with the "anti-alias pixel" effect activated. One can easily see the smoothing of the pixels. This is how I prep images prior to digitizing. My motivation is that shorelines are not pixel shaped. The look more like the smoothed shorelines. So, I elect to smooth shorelines prior to digitizing them.

Either way, the PGS vectors are impressive. They track the EVS vectors closely. There are some discrepencies, but they are minor. Last night, I loaded all 28 PGS vector files into Marplot, my mapping software. It took about 3-hours to download, prep, import and define layer attributes. Now, I am able to work with these vectors prior to digitizing from Landsat ETM+ imagery. Although the PGS vectors are stunning when one compares them to WVS, they do not resolve shorelines as precisely as I am able. Consequently, EVS lives! I will benefit from the PGS vectors, but my mapping will continue.

If any of my readers know the parties involved in developing the NGA PGS vectors, I would welcome the opportunity to use my EVS efforts to QC their efforts. Drop me a line with a contact or have them get in touch with me. If any of you would like pointers on how to process the NGA PCS files (28 total) drop me a line. I'll be glad to share what I have learned in working with them

Posted by Mr Minton on Wednesday, June 14, 2006 at 6/14/2006 11:48:00 AM | Permalink