How to Adjust PGS to EVS Precision: The Quest Continues
To do this post justice the reader should Left Click on the image and then select "All Sizes". You will be able to view the image at it's original size 1280 x 1024. The shorelines and map vectors are much easier to study.
PGS at 1:250,000 (Vinh, Vietnam)
This begins with the above split image. On the right is Landsat N-48-15 showing the area around Vinh, Vietnam. The image is at 1:250,000 or the same scale used by World Vector Shoreline (WVS). In my opinion, PGS shorelines are gorgeous at this scale. They are very precise.
PGS at 1:125,000 (Vinh, Vietnam)
I have been told by numerous people that work with Landsat ETM+ that this is the most reliable scale, 1:125,000, that can be extracted from Landsat. I know all about the limitations of this imagery (14.5 meters per pixel), but I use my eyes and it looks like one could zoom in even further. So lets try!
PGS at 1:62,500 (Vinh, Vietnam)
At this scale, 1:62,500, I still believe that the vector files that have been created from Landsat imagery are PGS files. They are consistently tightly following the shoreline (as defined by EarthSat algorithims). There are some clunky looking angles, but the overwhelming majority of vectors are close to where they should be.
PGS at 1:31,250 (Vinh, Vietnam)
At this scale the clunky vectors begin to appear with greater frequency. The smooth shoreline is not so smooth. But could PGS be more precise?
PGS at 1:15,620 (Vinh, Vietnam)
Now the clunky lines are occuring with greater frequency. The PGS vectors were never intended to be used at this level of resolution. The shorelines are intented to be used at that 1:125,000 or, at best, 1:62,500. PGS and WVS were never made to be used at this resolution. But, can these PGS vectors be improved upon? Yes! Landsat imagery begs to have the vectors that claim to track the shoreline actually track it.
PGS at 1:7,810 PGS Vectors (Vinh, Vietnam)
At 1:7,810 scale the PGS vectors kind of track the imagery depiction of the shoreline. Then comes Enhanced Vector Shorelines (EVS).
PGS at 1:7,810 EVS Vectors (Vinh, Vietnam)
The brown line is my EVS shoreline. The upper portion of the image tracks a sand bar that encircles a small lagoon. Many of the unneccessary vectors have been deleted. It is as if the digitizing algorithim stuttered. Almost all of the vectors have been adjusted. The adjustments are typically between 10 to 50 meters. Some might say that I need to back off. Just live with the 10 to 50 meter differences. But, I say Landsat depicts a shoreline and it is my job to determine it and then to place vectors that trace it. I call this effort EVS. Look at the final image (Select it, select "All Sizes" ) and you will see a shoreline that does justice to Landsat ETM+ 2000.
