Thoughts - When is a Shoreline a Shoreline? A Continuing Discussion.

Kyra Panagia - EVS Compared to NGA PGS

Comment posted by Anonymous:

Shorelines are usually created through stereoplotting or derived from surface models - rarely from monoplotting like you do. The problem with monoplotting is that your shorelines will be different depending on the tide, so your shorelines might very well be even more off in many places - especially at relatively flat areas and/or shallow water.

My response:

Anonymous, your observation concerning the use of stereoplotting and surface models providing an accurate approximation of a dynamic shoreline are well taken. If one had the imagery depicting the shoreline at various stages of tidal fluctuations during a set period of time, the methods you refer to would always provide the superior shoreline representation. However, after monoplotting 1,000s of kilometers of shorelines and comparing my EVS precision shorelines to NGA PGS precision shorelines - EVS shorelines track the Landsat ETM+ imaged shorelines more consistently then NGA PGS precision shorelines. My guess is that their method introduced unanticipated stutters, inconsistent shoreline identification and non-inclusion of water inundated areas.

EVS precison is not perfect, just better at tracking the visible shoreline more consistently then NGA PGS.

Comparison - EVS to NGA PGS, One More Time

Kyra Panagia - EVS Compared to NGA PGS

Enhanced Vector Shorelines are derived from Landsat ETM+ mosaics. When I carefully digitize an island shoreline using Landsat imagery as my base image, I create EVS precision vectors. This name describes an improved shoreline over World Vector Shorelines.

The NGA Prototype Global Shoreline claims to be a global vector shoreline derived from Landsat ETM+ mosaics, the same imagery I use. When I first learned of it, I thought to myself, "My work is done! MDA has produced the ultimate global vector shoreline. Well, they really haven't. It seems that their shorelines do not track Landsat's imaged shorelines. They are close, somettimes very close. But far too often, they are off, sometimes by 100's of feet.

It is my contention, if Landsat provides a clearly imaged shoreline, the vectors that describe that shoreline should be as close to the shoreline as possible. NGA PGS does a pretty good job, but when I compare their product to my EVS precision shorelines - mine are better at tracking the Landsat imaged shoreline.

Enjoy!

Thoughts - Zooming Futuna Island, Just For The Heck of It!

DigitalGlobe Imagery of Futuna Island Taken From Google Earth

Nothing special in mind. Just thought I'd zoom in on Futuna Island from 1:48,000 scale down to to 1:750.

Enjoy!

Thoughts - Changing Background Colors and Blend Options

The Effect of Blends and Backgrounds on LIIMs

I most often digitize from LIIMs using Global Mappers's Blend Mode called No Blend (Slide 1). No Blend shows the various land and water features as Landsat ETM+ mosaics intended them to look - somewhat natural. For most projects, this image works fine. However, atolls present some unique challenges - What is above water and what is below? What is shore vegetation and what is bare earth that looks like shore vegetation? Where does the land end and the reef begin? Like I said, unique challenges.

When I encounter these challenges, I use a couple of different options - 1) changing the background color to either Yellow (R-157,G-191,B-202), Pink (R-255,G-128,B-192), Light Pink (R-255,G-193,B-224) and Blue (R-157,G-191,B-202) and using two new Blend Modes - Difference and Color Burn. Let's talk about Difference first.

Tauere Atoll - Blend Mode Difference and Blue Background

Difference creates a soft looking false color image that makes certain atoll features stand out, for example the sand. It is also a great way to distinguish underwater features. I always switch between No Blend and Difference to visually confirm my work.

Tauere Atoll - Blend Mode Color Burn and Blue Background

Color Burn creates a sharp separation using false colors. The blue background and Color Burn allows for some potentially very precise digitizing of various island features. Using the other background colors, other than blue, gives a washed out effect. Not very handy for digitizing work.

My biggest challenge when working on an island mapping project is determining the shoreline - where the water meets the mostly dry land. Using the Global Mapper's Blend Mode and changing background colors is a great way to meet this challenge.

Enjoy!

Data - World Port Index Data to Download and Correctly Plotted

World Port Data with Southern Hemisphere Data Misplotted



World Port Data Showing Attributes



World Port Data with the Southern Hemisphere Misplots Corrected

I hate to mess up, especially when it comes to reworking perfectly good data. In my original post concerning World Port Index Data, I failed to notice that large portions of the southern hemisphere were misplotted. It turns out that a negative longitude should have read positive. In other words I had the East in the West.

Now is a good time for me to remind all of you, use this data at your own risk. I do the best that I can with the data, software and expertise I have. Almost all of the time, I do excellent work. Sometimes, though, I do misplot data.

The WPI data comes from NGA data, Pub-150. Initially, I had extracted the data from MS Access into MS Excel, loaded the file and reworked it so it could be plotted. Unfortunately, I messed up on data in the southern hemisphere.

I have reworked the misplotted points and have them positioned correctly. I understand if you are leery about the quality of this data, but I am almost certain that all of the misplots have been corrected. Regardless, the World Port Index data is available, in SHP format, for download at this link. Good luck with it. If you find problems with the data, let me know and I will correct them ASAP.

Enjoy!

How To Turn a Black Sea Transparent

Nisos Skiathos - LIIM with a Black Sea (1:90,000)

Let's begin with the LIIM of Nisos Skiathos. There are times I would like to switch off a range of colors or, for that matter, switch off any colors I wish to. I asked Mike at Global Mapper if a modification like this would be possible. He said that it seemed to be a fairly simple process and he would modify Global Mapper v9.0 to allow this color by color control.

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How To Create Transparent Seas

The process to switch a color or multiple colors off is simple. The image I used is a GeoTIFF 8-bit. Within the Overlay Control Center select the image and open it with Options. Select the Transparent feature and you will be given a palette of colors. This image contains 255 colors using the GeoTIFF 8-bit image option. Either use the shift-key to select a range of colors or the control-key and pick and choose any colors you want. I selected all of the colors that defined the black sea. Switching them off gave me the image below.

Nisos Skiathos GeoTIFF 8-Bit Transparent Sea (1:90,000)

Pretty slick, huh? The process to switch off the black sea and make it transparent took about 30-minutes to complete. I really like this feature. It allows for some pretty creative imagery analysis. For example, the burned area on Nisos Skiathos could be easy to isolate and study in greater detail.

Global Mapper's way of doing business - 1) Ask for a feature. 2) If it can be done, Mike will add the feature. If not, Mike will tell you straight up. 3) And the cost for the feature update - $0.

Enjoy!

Nisos Skiathos GR - And Another Sporades Island

Nisos Skiathos - LIIM from N-34-35_2000 (1:70,000)

Nisos Skiathos is the westernmost island of the Sporades. It is reported to be heavily forested with pine trees. However the ugly red splotch in the center of the LIIM is a burn signature. When a forest fire occurs on a small island, it puts all of the inhabitants at risk. This fire was restricted to the mountainous interior. It would have occured over 7+ years ago and I am confident organic ground cover has returned to the area. According to a Nisos Skiathos web site, the island is heavily populated with tourists during the summer months. They visit the old fortress at Kastro (NE), long stretches of sandy beaches and enjoy a festive nightlife in Skiathos town.

My perfect visit to this island would be off-season. I would spend my time exploring and visiting with the local folks. In the evening I would walk in the town looking at the shops and selecting a taverna to dine in. Then I would retire to my room overlooking the sea. I would relax on my balcony with a good book, a glass of 20-year old port wine, a Cuban cigar and soft music in the background. I would fall asleep at 1:00 AM, wake up at 5:30 AM and start all over again. Wow! Now that is living on the edge.

Nisos Skiathos - EVS Precision Marplot Map (1:70,000)

The map was created in approximately 4-hours. It was a fairly straight forward island mapping project. Nothing out of the ordinary. I am working on color schemes for my various map layers. The colors are still being explored. I have been using Marplot's text feature. One has the option of using five different fonts. You control the size of the text by selecting and dragging it until you are satisfied with the size. I have used Time New Roman font for this island mapping project.

Enjoy!