EVS-Islands

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

I have over 600+ Landsat ETM+ Orthorectified Mosaics that two summers ago I patiently downloaded and copied onto a series of DVDs. These mosaics cover all of the shorelines and oceanic islands throughout the world. It is an impressive collection. This collection, coupled with Global Mapper v9.01 (GM), allows me to load and view the individual mosaics as I desire. Each mosaic, even compressed in MrSID format, is typically 100 to 250MBs. Them is some big files!

Over a year ago I had a discussion with a reader who wished to work with these files to make his own maps. I described where he could download the files. But, alas, he said the files, even in MrSID format, were too large for his system. Was there a smaller file of just individual islands, he asked. Not to my knowledge, I guessed and went back to making maps of islands.

That was until this past month and my work in image mosaics. First I worked with DigitalGlobe imagery. Sadly, they have never responded to my product idea. Oh, well, so goes life. Lately, I've been working with Landsat ETM+ again. And the following is my latest idea - Landsat Island Image Mosaic or LIIM.

Greek and Turkish Islands - Landsat ETM+ Mosaics

Some of my earliest mapping efforts were of Greek and Turkish islands located in the Aegean Sea. This area is virtually cloud-free and the clarity is outstanding. However, it takes seven Landsat mosaics to cover the area. Using a raster export feature within GM, I experimented with various raster formats and came up with georeferenced JPG. Pixel size of each resulting LIIM is 14.5-meters, 300 DPIs and projection is Mercator. The resulting image is outstanding.

Nisos Limnos - Landsat ETM+ N-35-35_2000

I zoomed into my target area encompassing the primary island and created the georectified JPG. The above Nisos Limnos LIIM taken from GM gives the user the complete resolution power of Landsat ETM+ without the size problems. The above file, along with it's accompanying DEM, is only 7.2MBs.

Greek and Turkish Islands - SRTM Tiles

To really bring the Nisos Limnos LIIM to life, the SRTM data is the ticket. To cover the Aegean Sea one needs 83 individual SRTM tiles. Loads of data for most of us. Many of these tiles require some fixing, which is done using SRTM Fill (freeware) to fill holes. Once this data is loaded, GM allows for DEM creation. One is able to take the Nisos Limnos DEM and drape the Nisos Limnos LIIM on top and get a variety of 3D views of the island.

Nisos Limnos - SRTM N039E025

So I exported the underlying area into DEM format. This allows for some nifty looks at the island

Nisos Limnos - 3D View

Pretty cool! This is the Nisos Limnos LIIM draped over the Nisos Limnos DEM. All of this wrapped up in a 7.2MB package. I like it. How about you?

I should add that I have created 16 Greek and Turkish Island LIIMs. The following islands have LIIMs - Bozcaada, Gokceada, Nisida Fournoi, Nisida Gioura, Nisos Agios Efstratios, Nisos Alonnisos, Nisos Chios, Nisos Ikaria, Nisos Lesbos, Nisos Limnos, Nisos Pelagos, Nisos Samothraki, Nisos Skiathos, Nisos Skopetos, Nisos Skyros and Nisos Thasos. I intend to complete coverage of the islands of the Aegean before I head back to school on Jan 03, 2008.

Enjoy!

Labels: DigitalGlobe, Global Mapper, Landsat ETM+, LIIM, Limnos Island, SRTM

Posted by Mr Minton at 12/26/2007 09:04:00 PM | Permalink | Comments | links to this post

1) The first image is DigitalGlobe's (DG) coverage found in Google Earth (GE). Using GEs Path Tool, I digitized over 3/4 of the islands shoreline. The digitized shoreline from a DG image is considered to be EEVS precision, meaning scales below 1:12,500 is routinely possible. Once I had completed my GE phase of this project, I saved the completed EEVS shoreline with cloud-obscured gaps identified for later work. I was able to then load this KMZ file into Global Mapper (GM)

2) The balance of the shoreline was digitized using WRS imagery, specifically those identified as path 016 row 056. The imagery is packaged in 257MB TAR files. Once downloaded and unzipped, one can select from a number of TIFF images. I used nn40 tif image.

3) With the shoreline complete, I systematically added layers of information (name labels, land polygon, streams, contours). The SRTM image, N05 W088, served a double purpose. First, I was able to use GMs "Generate Contours" routine to create contours. In addition, The SRTM image was used to create a shaded relief image of Isla del Coco.

Isla del Coco - Island Image Georectified JPG

Now for some data for all of you with mapping packages. I have zipped 9-layers of data that makes up the vector files for this project. The layers include: shoreline, streams, contours, name labels. Using GM, the zipped shapefiles load in about 2-seconds.

The second package contains a georectified JPG imag of the island and a DEM formatted file of the island. It should be loaded first with the JPG draped over it. You can do some neat 3D work with this combination of images.

Isla del Coco - 3D View SW to NE

If you load it with various vector layers, you can see them draped over the landscape of Isla del Coco.

Now for the "Treasure Island" stuff. According to Wikipedia, there are at least 3 treasures buried on this island. Pirates used the island as a hideout for years. Supposedly, Robert Louis Stevenson used Isla del Coco as inspiration for Long John Silver's Treasure Island.

Enjoy!

Labels: DEM, DigitalGlobe, Global Mapper, Google Earth, SRTM, WRS

Posted by Mr Minton at 10/27/2007 04:20:00 PM | Permalink | Comments | links to this post

Verde Island - Landsat N-51-10_2000 Image (1:31,250)

Verde Island - Marplot Map (1:31,250)

Verde Island is located between the islands of Mindoro and Luzon in the Philippines. It is a project of opportunity, a random island in a country of thousands of islands. So what is the story. It seems this passage between the two large islands is an important west-east route. It seems that a Spanish galleon had problems off of Verde Island, sunk in about 60-m. Divers today still find booty that is dated to the time of this ship's sinking. Most divers swim around a look at the reef and it's myriad of lifeforms. This island is 7-km by 5-km and has a number of small villages scattered about.

I'm making my map labels pretty. The Marplot generated labels were functional, but plain. I like the look of these custom labels. As I stated previously, they are one size only. It would be nice to have the shrink and expand based on the map scale. I like my text fox and entry. The contours were generated from SRTM 61-10 using Global Mapper's contour generation function.

Enjoy!

Labels: disitize, EVS, Global Mapper, island, Landsat, Marplot, SRTM

Posted by Mr Minton at 6/19/2007 12:34:00 AM | Permalink | Comments | links to this post

Underneath SE Asia

Guess how? Hints - Landsat ETM+ N-47-20_2000, SRTM v3 Z_56_8.tif and Global Mapper 3D View.

Enjoy!

Labels: Global Mapper, Landsat, SRTM

Posted by Mr Minton at 5/29/2007 07:29:00 PM | Permalink | Comments | links to this post

Hatutu Island - Digital Globe Image (1:25,000)

Hatutu island - Marplot Map (1-25,000)

Let me begin by apologizing to the fine folks at DigitalGlobe. Their imagery for this island is actually depicted by the bottom half of the image composite. The upper, grainy image is a thumbnail of imagery they have in their archive for this island. So, if I would have had the northern imagery to combine with the southern portion of the island, you would be looking at a nearly cloud-free image of Hatutu Island, which isn't cloud-free very often.

However, the shoreline I was able to fashion from this composite is excellent, based on the available imagery. The shoreline would allow researchers the opportunity to plot information onto the island surface with reasonable accuracy. Let me modify that, with excellent accuracy based on currently available mapping.

Hatutu Island - West to East Profile Using SRTM Data

I'm still waiting for my funding source - merely a living wage, access to Digital Globe's extensive archive of Hi-Res imagery and then get out of my way and let me make maps to share with the rest of us FOR FREE. That's all I need. Any takers?

Enjoy!

Labels: DigitalGlobe, EVS, French Polynesia, Global Mapper, island, Marplot, Marquesas, SRTM

Posted by Mr Minton at 5/25/2007 06:54:00 AM | Permalink | Comments | links to this post

Eiao Island - Landsat ETM+ and Digital Globe Hi-Res

From Landsat (left panel) to Digital Globe Hi-Res (right panel).

Eiao Island - Marplot Map Original and Improved

From EVS precision shoreline extracted from a cloud-obscured Landsat ETM+ image to EVS precision shoreline extracted from a cloud-free Digital Globe Hi-Res image.

HAPPY ONE-YEAR ANNIVERSARY

EVS-ISLANDS

At 1415 April 2, 2007 my blogsite became one year old. It consists of 296 posts covering a wide variety of topics, most providing details of islands scattered throughout the world.

My mapping skills have improved. I began mapping shorelines only. Yet, I quickly moved to including more and more details. Now, my maps contain upwards of 16-layers of information.

Anytime I mapped a high island, elevation contours were beyond my expertise. Now, using SRTM elevation data and Global Mapper contour-creation module, my maps include elevation contours.

My visitors keep coming back, just under 20,000 this first year. They come from GIS and "arm-chair-traveller" backgrounds. They come from the energy, education, environmental, governmental and private sectors of society. They live in over 152 countries. And they view 100+ pages a day. They seldom criticize and often encourage. Occassionally, they ask to use my data and I always say, "Yes.".

I look forward to another year filled with many more discoveries.

Thanks for your support!

view Eiao Island on Google Maps

Enjoy!

Labels: Digital Globe, EVS, Global Mapper, island, Landsat, map, SRTM

Posted by Mr Minton at 4/03/2007 06:31:00 AM | Permalink | Comments | links to this post

Rapa Island - ISS Image ISS004-E-12979

I have worked on this Rapa Island project off and on for a number of months. It is a challenge because: 1) It is a high island and that means contours. Up until a month ago, I had not figured out how to easily plot contours. Using SRTM imagery and Global Mapper, it is a relatively simple task. 2) Clouds! Now that is a major problem when digitizing from a cloud obscured image. Your work is typically one guess to another guess or you are forced to scrounge whatever imagery you can gather to fill in those cloudy blanks.

Rapa Island - SRTM Image With Voids

Those sheer walls that show up in the above image are cloud obscured areas. The shuttle mission that compiled these SRTM files couldn't gather elevation data through clouds. Some folks are systematically, doing their best, to fill in the voids. Progress is slow and with mixed results. The real champions of the void fillers are the flight simulator people. They are trying to construct their 3D world to fly over.

Rapa Island - Shuttle Image 3D With Voids

So this is what one gets when you drape an image over the SRTM data with voids. Peaks peak and valleys valley. Everything looks as it should. Everything, that is, except those damn voids!

view Eiao Island on Google Maps

Enjoy!

Labels: 3D, Global Mapper, SRTM, voids

Posted by Mr Minton at 3/25/2007 07:27:00 AM | Permalink | Comments | links to this post

Pulau Romang Island Group

I've been working on this group of islands for the past few weeks. All of the layers of information are digitized. This week I will bring the digitized files into Marplot and construct my map. After the map is complete, I will create contours. Finally, I will publish the completed images.

Improved Rapa Island Shoreline and Contours

This project is also in the final stages. I discovered Digital Globe hi-res imagery on Google Earth covering most of the island. The improved shoreline is complete. I will create as many additional layers of information as the imagery will allow. The western portion of the island is cloud covered. DG does have a cloud-free image. Maybe they will let me use it? Unfortunately the SRTM data covering the island has large voids that I will have to extrapelate the course of the contours. I will need to find a reasonable topo of the island (fat chance!) or do my best guess-timation of the missing contours. It should be a challenge.

Cabrits NP Dominica Island

This is part of a viewer's senior project. You all know that I do work for free. If it is non-commercial, within my abilities and the time-frame is mutually agreeable, I'll create an EVS precision project for you to use. It turned out this area has Digital Globe imagery to work from. Consequently, the land use layers were detailed and complex. The SRTM data had a void that I had to guess-timate the contours. For the purposes of this student's project. the time constraints and the fact that I was working in uncharted areas of expertise, the guess-timate method was sufficent. I worked on this project off and on for over two weeks and am pleased with my efforts.

Other projects being worked on are Lindesfarne Island, UK and The Three Maria's located off the western coast of Mexico.

So many projects and not enough time.

Enjoy!

Labels: Digital Globe, digitize, EVS, Global Mapper, Google Earth, map, Marplot, SRTM

Posted by Mr Minton at 3/19/2007 06:06:00 AM | Permalink | Comments | links to this post

Comparison of Four Different World Vector Shorelines

If you look at most commercial digital atlases, their data is based on Operational Navigation Chart (ONC) data, which was originally compiled and maintained so that pilots could use these maps as reference tools when viewing features from 20,000 feet. They worked well for their intended purpose and were reasonably maintained. They were largely fashioned from pre-satellite data, much of it derived from aerial photography dating from WW-II through pre-Vietnam. Any cartographer worth their mapping "salt" will tell you that much of the data is, at best, only moderately accurate. ONC shorelines are close to actual shorelines, but not very close. The ONC shorelines were never intended to mirror the actual shoreline. I mean the scale is 16-miles to the inch!

So from this data source a product called Digital Chart of the World (DCW) was produced. Every atlas company producing small scale mapping uses some or all of the DCW data. Since my area of focus is global shorelines, I can state with certainty that if DCW shorelines are used in a map product, those shorelines are only moderately accurate. But for many map users, moderately accurate works. My Michelin maps got me from city to city and allowed me to navigate with a solid degree of certainty.

World Vector Shorelines, at a scale of 1:250,000 (4-miles to the inch), were fashioned from Tactical Pilotage Charts and other similar sources. Their shorelines are more accurate than DCW/ONC shorelines. However, they also more often miss the shoreline than track it.

Landsat ETM+ 2000 Coverage

Now we get into the realm of space-based mapping. With a virtually cloud-free image of earth, Landsat gives us a georectified imagery base from which extremely precise shorelines can be extracted. And it was done! The Prototype Global Shoreline, using a carefully researched, crafted and tested digitizing algorithm created a global shoreline that can be used at between 1:125,000 to 1:62,500 scales. If DCW/ONC shorelines are moderately accurate and World Vector Shorelines are extremely accurate, Prototype Global Shorelines track the shoreline with a high degree of reliability. That is until one zooms in and studies the PGS vectors as they relate to the Landsat image from which they were derived.

EVS and PGS Vectors

Upon closer inspection, they do not track the shoreline very often. They are typically anywhere from 15-meters to 200-meters off-center. Their vectors have a habit of "stuttering" unneccessarily as can be seen in the above image. They also do not account for large sections of shoreline that is water innundated, per NIMA's request.

EVS Would Digitize the Water Inundated Areas

EVS vs PGS Precision

Finally I get to my product, Enhanced Vector Shorelines (EVS). All of my shorelines are done by hand. The vector plotting errors inherent with this methodology are minimal compared to PGS errors. EVS provides the most accuracte shorelines extracted from Landsat ETM+ 2000 mosaics. Unfortunately, that only includes the coast of Morocco, Taiwain, Madagascar, Baja California, Caspian Sea and many islands scattered throughout the world.

Now to repeat the question I posed at the beginning of this post, "Who cares?" Should the world shorelines be mapped at EVS precision? Is the PGS, which is pretty good, sufficient for most projects? Is pretty good, good enough?

I think that a world shoreline at EVS precision would be extremely useful. I believe, that properly constructed, it would become the base mapping data for military, government and private sector projects for years to come.

I know I have a large number of GIS savy readers. What do you think? Should the world be mapped at EVS precision? And if so, why? Feedback would be appreciated.

Enjoy!

Labels: DCW, digitize, EVS, Global Shorelines, Landsat, ONC, PGS, SRTM, WVS

Posted by Mr Minton at 3/11/2007 04:50:00 PM | Permalink | Comments | links to this post

Guadalupe Island - Landsat Image N-11_25_2000 (1:200,000)

During the later part of December 2006, I worked on the Guadalupe Island project. I began with a Landsat image. After a quick, yet thorough, inspection, I determined that the Landsat image was not satisfactory for an EVS quality project. First, and foremost, far too many clouds obscured the island.

Guadalupe Island - Digital Globe Image From Google Earth (1:200,000)

So, I visited Google Earth and found a great 1-meter resolution Digital Globe image. I used it to digitize my various layers of information. Around the same time, I began using SRTM data to construct contours for many of my completed projects. I used the following SRTM data to construct contours for Guadalupe Island.

Guadalupe Island - SRTM Image N29W119 and N28W119 (1:200,000)

From these images, using Global Mapper, contours were quickly and easily generated. I knew Global Mapper had a 3D feature and if you have loaded the proper data, SRTM for example, 3D images can be easily rendered. I had never used it.

Guadalupe Island - TerraMetrics Image Loaded Into Global Mapper (1:200,000)

First you need the image you will drape over the SRTM data. This image must be loaded on top of the SRTM data. So I loaded the Digital Globe images of Guadalupe Island into Global Mapper. All four of the images were at a scale of 1:62,000.

Global Mapper - Select 3D Option

To select the 3D option, you merely point and click.

Global Mapper - A 3D View of Guadalupe Island

And there you have it - a 3D view of Guadalupe Island. Needless to say, you can control the vertical exaggeration, ocean depth and other aspects of the image. The image can be tilted, twisted, zoomed and other manuvers. You can snap a picture at each juncture.

Guadalupe Island 3D View From SW to NE

This view shows a deficiency of the SRTM data. If something obscured the elevation data gathered by the Shuttle, you are left with what is called a void. There is data available that attempts to fill the voids with reliable alternative elevation data. A couple of areas along the western side of Guadalupe are actually voids. The elevation data at those voids are greatly exagerated. As I gather more SRTM data, I will replace the SRTM voids with SRTM with filled voids.

Guadalupe Island - 3D View From S to N

Guadalupe Island - 3D View Detail of Cypress Groves

The 3D views are easy to make and quite informative in the elevation details they display. It makes 1-meter resolution imagery come alive.

Enjoy!

Labels: 3D, contours, Digital Globe, elevation, Global Mapper, Google Earth, island, Landsat, SRTM

Posted by Mr Minton at 3/03/2007 08:40:00 PM | Permalink | Comments | links to this post

1. First you must select a target. Since I map islands, my target island is Sadoga-shima JA. With the selection of the target, you need to gather the lat/lon coordinates for the NSEW extremities of the island. Here I gather the coordinates using Google Earth.

2. Now you head into the SRTM3 version 2 area to snag your SRTM files. I use an index map that I have on my desktop to determine the region from which I will download my files. The region I need is Eurasia.

3 & 4. I need two files to cover my target area. the first is N37E138.hgt.zip and N38E138.hgt.zip. These are relatively small files (778 KB and 157 KB) but the display is stunning. I download the files to my desktop and then place them into my EVS Islands work area.

5. After the files are securely stored, I open Global Mapper (GM) which will be my contour generating software. First I select File menu and Open Data File(s)...

6. GM allows for importing of multiple files. I select both files. I do not have to unzip them as GM handles that task as well. I merely select them, select Open and the files load.

7 & 8. The load is fast. I happen to be using a display called HSV Shader. I can select certain colors and have them shade to give me my choice elevation display. Once my SRTM .hgt zip files are loaded, I zoom in to include only my target area on screen. It is not necessary, but it is my work habit.

9. Now for a slightly funky step. It is my experience that SRTM elevation data reads elevations in the open ocean where there is no land. I suspect it is reading the sea level, which is higher then SRTM's 0 meters level. (I think this makes sense.) Anyhow, if I change the water level to 10 meters within the Configuration Menu/Vertical Options, most of the problem contours are handled.

10. Now comes the fun part, making contours. Select File and Generate Contours.

11. You now define certain characteristics of your contours. This Contour Options is the default. I usually stay with the default, unless something really wacky comes up. 50 meter intervals, although busy at 1:337,200, looks very good at 1:50,000. I typically Generate Spot Elevations at Min/Max Elevations. The two choices below it are default options.

12. I didn't display the Simplification Option. It is self-explanatory - you either get smoother or less smooth contour lines (more or less vertices). The Contour Bounds gives one lots of choices on how to select your target area. Since I only include my target area on my screen, I select the second option. Sometimes I Draw a Box... around my target area. Select OK.

13 & 14. Select OK... I had to capture this next screen fast. The contour creation process typically lasts about two to three seconds for my islands. Very large areas will take a greater amount of time.

15, 16 & 17. And here are some of the contours. This display, because of the scale, shows only a few major contours. However, once you zoom in, all of your newly created contours are there to behold. There is cleanup that needs to happen. Sometimes contours extend across open water due to SRTM misread. Also a few scattered 0 meter contours should be selected and deleted.

And that is how you are able to use Global Mapper to create contours. It is easy, fast and mostly free, except for the cost of Global Mapper (about $200).

Enjoy!

Labels: contours, Global Mapper, hgt file format, map, SRTM

Posted by Mr Minton at 2/09/2007 07:16:00 AM | Permalink | Comments | links to this post

Clarion Island - Marplot Map With 40-meter Interval Contours (1:35,000)

I had someone checking out my Clarion Island map and I decided to place contours derived from SRTM data. The SRTM data wants to construct contours over water. The entire northern edge of Clarion had contours extending over water. I moved them back onto land, but I doubt if the cliffs on the northern side of the island are as steep as they are shown on this map. Oh well...

Enjoy!

Labels: Global Mapper, island, Marplot, Mexico, Pacific, SRTM

Posted by Mr Minton at 12/16/2006 06:22:00 PM | Permalink | Comments | links to this post

Socorro Island - Landsat Image Cleaned

Socorro Island - Marplot Map (1-100,000)

Socorro Island - SRTM-30 with Contours (50-meter interval)

Socorro Island - Google Earth Southern Detail (1-25,000)

Socorro Island - Marplot Map Southern Detail (1-25,000)

I took my original Socorro Island project and decided to add 50-meter interval contours.  The process in Global Mapper is simple.  First you need to load the appropriate SRTM-30 file which I snag from a NASA site.  I get SRTM Version 2, which is the latest and greatest.  The two files that makeup Socorro Island are titled N18W112.hgt.zip and N18W111.hgt.zip.  GM allows these files to be loaded while zipped.

Once loaded I select "Generate contours..." from the File menu.  I selected the default of 50-meter intervals.  I enclose the area to create contours from and Enter.  The contours are created within seconds.

SRTM is a fairly rough cut, consequently the contour closest to the shoreline wabbles in and out of the shoreline.  The last step is to manually adjust this shoreline.  All of you mapping pros wince when I say that I adjust manually.  You appreciate that this adjustment is a W.A.G. (Wild Ass Guess) based on experience and practice.

What you see above is both the entire island with 50-meter contour intervals and a detail of the southern end of the island.  I used Google Earth imagery of Socorro Island to create the exellent shoreline.  I call it GEVS - Google Earth Vector Shoreline.

Like I have said, this creating of contours business is a snap with Global Mapper.  Try it, you'll like it.

Enjoy! 

Labels: EVS, Global Mapper, SRTM

Posted by Mr Minton at 12/05/2006 09:11:00 PM | Permalink | Comments | links to this post

Makatea Island - Marplot Map with Contours North (1-31,250)

Makatea Island - Marplot Map with Contours South (1-31,250)

Makatea Island is an old project.  It is also an island that generates alot of interest.  I think the reason so many of my visitors view this island is because it is one of the few high islands within the Tuamotus.

Having recently discovered the ability to quickly create contours using SRTM data, I decided that Makatea Island could use contours. I downloaded the appropriate SRTM tile and loaded it into Global Mapper.  I then zoomed into the island, selected "Create Contours", selected 20 meter intervals, pressed "Enter" and created the contours.

The contours created on the northern end of the island extended into the ocean.  I had to reshape them to fit into the actural shorelines.  It seems to be a problem with SRTM data.  Or it could be a problem with footing SRTM data with Landsat ETM+ imagery.  Seeing that 95% plus of the contours appear to be plotted where they might belong and the problem of contours extending into the ocean is typically located along a small portion of the shoreline the problem seems restricted.  I really need to explore it in greater detail before I determine the causes of the problem.

The Maketea Island map with contours is good.  Those of you that require contours for this island, know that I have them and will share them.  Just drop me a line and I'll fix you up with any of the layers you might require.

Enjoy!

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

Posted by Mr Minton at 11/28/2006 09:52:00 PM | Permalink | Comments | links to this post

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

Comparison of EVS, PGS, WVS and SRTM (1)Shorelines

A picture is worth a thousand words. The above image contains a small segment of Eiao Island FP. The scale is 1:12,000. What are visually displayed are the shorelines of various global shorelines (PGS, WVS and SRTM (1)) as they compare to my own EVS shoreline. They all fall short of depicting the actual shoreline and that is to be expected. A shoreline is a dynamic geologic entity. It is constantly in motion. There will never be a penultimate map (a static entity) that depicts a global (dynamic) shoreline. With that said, which of the four shorelines works best for your needs. All four shorelines have their uses.

The World Vector Shoreline, "old reliable", works for most mapping needs at a scale of 1:250000 or above. When you work above 1:2000000, the map becomes too busy. But between those two scales, WVS works fine.

Prototype Global Shoreline, when completed, will be "THE" map file for work from 1:62,500 up to 1:1,000,000 scale. It will provide details that will make WVS look like a clunky jalopy compared to a sleek race car. PGS will impact every country in the world. It will require a country-by-country acceptance. It will cause nations to redefine maritime limits and that is not an easy notion for nations to agree upon. Nations will gain or lose valuable real estate because maritime base lines and economic zones will be shifted because PGS shorelines will shift. If the shift results in a lose of real estate, my suspicion is the losing nation will not buy the new boundary. What an exciting proposition for the global community. Much of the above comes from a source within NGA that has the enviable task of completing this monumental map file.

SRTM (1)(SWBD) shoreline was added to show how far this vector mapping program has advanced. It is a solid vector map file that improves mightily upon WVS, but it does not accomplish the precision that is found in PGS. However, again from my source in NGA, there is a more precise global data source within SRTM. It is SRTM Level-2. It is available for the US today, but NGA has access to global coverage at the level-2 precision. I am purposely vague on SRTM Level-2 as I have not done much work with it, but I am certain it will perhaps rival PGS when released to the eager public.

Finally, my own Enhanced Vector Shorelines effort and how it compares with the other three shorelines. I like to think that EVS is the most accurate of the four, but that isn't quite so. The three are global in scope and mine covers islands and some shorelines. The places I have mapped at EVS resolution are more exact in depicting the actual shoreline than any of the other three shoreline sources. My ultimate goals with EVS is to see all shorelines mapped at that level of precision, to develop a consistent decision-making process as to map or not to map certain features and to bump this effort up into a legitimate concerted, well-funded effort that will result in a timely completion of the project within 2 to 3 years.

EVS, in my opinion, is the ultimate map file that can be extracted from Landsat-7 ETM+ 2000 imagery. When 1-meter resolution imagery is released and the coverage is global, the new and improved ultimate map could be created, EEVS (Extremely Enhanced Vector Shorelines). Until then, I will keep myself busy working on my labors of love – creating shoreline maps of islands.

Enjoy!

Labels: EVS, Landsat, map, PGS, SRTM, WVS

Posted by Mr Minton at 7/05/2006 11:35:00 AM | Permalink | Comments | links to this post