Tepoto Nord FP - A Redo of a Redo of a Small Coral Island

Tepoto Nord FP - Landsat Image from S-07-10_2000 (1:20,000)

Tepoto Nord FP - ISS002-E-8862 Image

Tepoto Nord FP - EVS Precision Map (1:20,000)

My first map of Tepoto Nord was completed on March 31, 2006. I used Landsat as my base imagery. Most of my finish work was done using Marplot, a fine poor-man's GIS program. In December 2006 , I came upon the ISS image of Tepoto Nord. I decided to redo my original work using the ISS imagery to digitize from.

I look at my completed Tepoto Nord mapping project today and contemplate how far my map making skills have progressed. My digitizing of shorelines, vegetation and reefs remains fairly consistent. I routinely work at between 1:12,000 to 1:8,000, depending on my base imagery and the ultimate objective for my map. I am content to map four to five layers of information taking what Landsat is able to provide. The first time I mapped this island, I remember being frustrated by the Landsat imagery. The odd colors and blurred appearance of the island made digitizing problematic. Eventually, I came upon the ISS image and was able to redo my mapping of this small island in a more satisfactory manner. I reposted the map and base imagery in December 2006 and gave this small island no more thought.

That is until I received a question from an EVS Islands reader. He wanted to know everything he could about this small island. I answered that he should contact Alex W du Prel, publisher of Tahiti-Pacifique magazine. If anyone could give information about this small island, Alex is the man. After answering the reader's question, I checked out my map of the island. Unsatisfactory! The map presentation choices I make today are far superior to those I made in 2006. I decided to redo my redo of this small coral island.

Tepoto Nord FP - DigitalGlobe Image from Google Earth (1:12,000)

Tepoto Nord FP - EEVS Precision Map (1:12,000)

I checked out Google Earth, as almost all of the islands within the Tuamotus are covered by DigitalGlobe's hires imagery. Sure enough, Tepoto Nord has excellent, cloud-free imagery from which I could redigitize various layers of information with a high degree of confidence. Seven layers of information later my redo of the redo is done. Since I have no designs to offer the map for commercial purposes, I decided to use DigitalGlobe imagery as my base imagery. I have worked on this redo of a redo for about two weeks. Not because it was particularly difficult, but I've been busy with school. Finally, I have a Saturday with no pressing projects. Only this, to finish my Tepoto Nord FP map. Pretty nice, huh?

Enjoy!

Motu Iti FP - Smaller is Quicker

View Motu Iti FP in a larger map

Motu Iti FP - DigitalGlobe Image from Google Earth (1:10,000)

Motu Iti FP - EEVS Precision Map (1:10,000)

According to widely accepted geographical feature identification practices Motu Iti and the rocky islets to the east are classified as islets (> 1 sq km). They are still defined as islands for the purposes of claiming Exclusive Economic Zones (EEZs), sea level to seafloor ownership encompassing a radius of 200 nm or 370 km from this island's shoreline. Interesting as this might be, it is not the reason I mapped these islets. Yesterday, I needed a break from the Komodo Islands project and these islets looked like a good option. I like the Marquesas and these are a part of the Marquesas.

There was nothing especially challenging in the shoreline mapping of these islets. The DigitalGlobe imagery is exceptional. I did preliminary shoreline mapping in Google Earth and finished the project up using Global Mapper. I've spent about 4-hours from start to finish which is par for the course when mapping a simple island shoreline.

Now for my guess work. The main islet, Motu Iti, has scatter vegetation on it. My source, Vegetation of the Tropical Pacific Islands found in Google Books, states that three types of low lying vegetation are found on the islet (Perlman, unpublish notes, 1989). The main islet is said to be 220 meters high. Based on this unsubstantiated elevation, I guesstimated 25-meter contour intervals using visual interpretation of the base imagery. I was unable to use SRTM coverage for these islets as it is of very poor quality. It would be nice to have side views of these islets, but alas, no side views were turned up in my research. Consequently, the elevations are educated WAGs (Wild A...d Guesses).

I'll rest up today and spend time with my wife, doing long overdue honeydos. She will be happy and so will I.

Enjoy!

How To Digitize EPIP's Four Atoll Layers

What is EPIP?

Enhanced Vector Precision Island Polygons - Using Landsat ETM+ ortorectified image mosaics as my base images, I digitize various layers of information, most typically from islands. I use Landsat ETM+ because: 1) It is free. 2) It is typically cloud-free. 3) It is consistent in quality. 4) It covers the earth. 5) It is virtually copyright free. This is the degree of precision over 8,000 South Pacific island polygons have been digitized to. This level of digitizing precision over such a broad expanse (South Pacific) is quite an accomplishment. What does this level of digitizing precision entail? What are the layers of information being captured?

Atoll Digitizing - First Layer Vegetation (Hi-Lo)

The first layer I digitize is vegetation. Working at a scale of between 1:25,000 to 1:15,000, I carefully digitize layer outlines. Working with the vegetation layer, I have been known to make a number of vegetation classifications. For the purposes of EPIP, I make one classification - Vegetation (Hi-Lo). This broad classification focuses primarily on land vegetation. I am reasonably certain I digitize some patches of reef vegetation as well.

Atoll Digitizing - Second Layer Island Polygon

My second layer of information is the island polygon. As the name implies, this should be any above-water land feature. When digitizing an atoll made up of many small motus located on a complex reef that is often awash the difference between above-water, reef awash and below-water can get fuzzy. It is within this layer that I am certain I include reef features that are either awash or just below water. In this layer, I prefer to digitize too much as opposed to too little. Perhaps the next generation of Landsat imagery will allow for a clearer land vs reef determination. Until then, I'll digitize in as consistent a manner as possible.

Atoll Digitizing - Third Layer Reef Shallow

This is another layer that I have used a number of classification. For the purposes of EPIP, whatever is visible (shade of blue) that I have not classified as a island polygon, makes up my Reef Shallow layer. This layer on the outer reef edge is typically defined by waves and/or a faint blue area along the shore. The inner reef shore also contains this blue area in varying shades and thicknesses. All of these blue areas are classified as Reef Shallow for the puposes of EPIP.

Atoll Digitizing - Fourth Layer Reef Deep

The final layer is Reef Deep or the central lagoon. It is basically everything within the atoll that isn't an island polygon or reef shallow. A crude classification, but it works well for EPIP.

I do all of my digitizing using Global Mapper. It is: 1) dependable 2) fairly inexpensive 3) simple to use 4) produces consistent product and 5) is serviced by Mike, absolutely the best customer service/owner of a product.

Atoll Digitizing - EPIP's Four Atoll Layers

And there you have it, EPIP's four atoll layers in all their glory. I'll share a few of my recently completed atolls with you. North is up and I realize they are unfinished maps without lat/lon, titles, north arrow and such, but they make the point, EPIP is a quality product.

Tahanea Atoll - EPIP (1:200,000)

Motutunga Atoll - EPIP (1:100,000)

Tunake Atoll - EPIP (1:50,000)

Tepoto Atoll - EPIP (1:25,000)

Enjoy!

Arutua Atoll FP - Beautiful Atoll and Long Mapping Hours

Arutua Atoll FP - Base Image From Landsat S-06-15_2000 (1:170,000)

Arutua Atoll FP - EVS Precision Map From Landsat S-06-15_2000 (1:170,000)

According to a Wikipedia entry, Arutua Atoll has a population of 500 with the majority living in Rautini Village. These hearty souls earn their living off of copra, fishing and pearling.They do have a small airfield located on their island.

Let's talk about what went into the construction of this map. I worked in excess of 12-hours on this map over a period of 4-days. The excessive amount of time devoted to this project had to do with the size of the atoll (31-km by 24-km). This map consists of 812 unique features. The majority of these unique features are motus (small island polygons) and coral heads within the lagoon. The trick to digitizing this atoll is determination, patience and cloud-free imagery. I initially worked off of the Landsat ETM+ mosaic, digitizing at scales between 1:25,000 to 1:12,5000. The digitizing process was tedious and tiring, but the final map looks great.

Arutua Atoll FP - Rautini Village From DigitalGlobe Image (1:6,800)

Arutua Atoll FP - Rautini Village in Other Precision Map From DigitalGlobe Image (1:6800)

Just for the fun of it, I digitized Rautini village using a DigitalGlobe image from Google Earth as my base image. The village took about 2-hours to complete. I added the road layer as a bonus feature.

All in all, I am pleased with this series of maps and I hope you find them interesting.

Enjoy!

Thoughts - My Progress at Mapping the Tuamotus

Tuamotu EVS Precision Mapping Progress

It has been nine days since my last post. What have I been doing? Keeping up with my summer duties - "honey do's", watching and entertaining my grandchildren (9 and 6 years) and mapping the Tuamotus. My goal this summer was to complete all 4 layers of EVS precision mapping for each of the 76 islands within the group - island polygon, vegetation, shallow reef and deep lagoon. To date 59 islands are complete. What exactly does that mean?

76 islands is not quite accurate. The Tuamotus are made up primarily of atolls. Each atoll has a number of islands, motus, to be exact. Just how many? A preliminary count puts the number of motus at approximately 5,640. Those are above water land. If the motu contains vegetation, I create a vegetation polygon. That means another 1,100 polygons to create (about 20% of the motus contain significant vegetation). Each atoll is surround by a shallow reef and an interior deep lagoon. However many of these interior lagoons are peppered with coral heads. If they show up on my base imagery, I map them. Probably another 2,000 polygons. All in all, I have to digitize 8,740 polygons, at least, to complete my summer project.

I have finished 59 atolls leaving me only 17 atolls to map. That is the good news. Now for the challenging news. Those 17 atolls will contain about 60% of the remaining polygons. All I have left to do is digitize another 5,240 polygons and I'll be finished.

If that seems like alot, it is. However, when this island group is mapped to EVS precision I will have accomplished my summer goal. It might be December 2008 before I complete my summer goal, but complete it I will. Wish me luck and...

Enjoy!

Mataiva Atoll FP - Unwelcomed Treasures

Mataiva Atoll - Google Maps

Mataiva Atoll - Landsat Image S-06-10_2000 (1:50,000)

I have looked at this atoll a few times and each time I decided to not digitize it. The reticulated lagoon represented many hours of digitizing. I knew the finished map would look great, but I just didn't want to do the work. Besides the lagoons near surface coral formations, the outer reef is raised and consequently much of it needed to be digitized into an island polygon layer. A challenge that I took up today. After four hours of digitizing and map composing, I'm finished.

Mataiva Atoll - Raised Reef (WikiMedia Commons)

This photo shows the raised reef of Mataiva Atoll. In the distance is a smaller motu. It makes for a pretty picture, but a digitizing challenge.

Mataiva Atoll - EVS Precision Map (1:50,000)

And here is the finished EVS Precision map. It is an attractive composition as well as an excellent depiction of the atoll.

Now for a little about this atoll and the inhabitants unwelcomed treasures - submerged phosphates. These deposits have been known for some time, but the inhabitants have resisted the mineral extraction of these deposits. Too many Pacific islands are a mess because phosphate extraction was vicisously pursued with little thought to the island's future. Hopefully, the inhabitants of Mataiva Atoll will continue their strong resolve to not exploit these submerged phosphate deposits.

Enjoy!

Hikueru Atoll FP

Hikueru Atoll - Google Maps

Hikueru Atoll - Landsat Image S-07-15_2000 (1:70,000)

There are times Landsat ETM+ island imagery is obscured by clouds. That is when I go to plan ISS or International Space Station imagery. One is not guaranteed that cloud free imagery will be available, but that is where I search for quality imagery.

Hikueru Atoll - ISS Image ISS002-E-8866 (1:70,000)

In the case of Hikueru Atoll, ISS002 snapped some great cloud-free images of Tuamotu atolls. Hikueru Atoll is covered by the above image. Using the above two images I was able to create my finished map of Hikueru.

Hikueru Atoll - Other Precision Map (1:70,000)

This mapping is part of my on going effort to map the islands of the South Pacific at EVS Precision or better. Other Precision is always EVS Precision or better. The map was finished using Marplot mapping software.

Hikueru Atoll is covered by a brief article in Wikipedia. As of the 1988 census, 124 people live on Hikueru. They earn a living from copra, fishing and pearls. The atoll does have an airport, which can be seen in the ISS image, that was built in 2000.

Enjoy!

Data - 78 Tuamotu Atoll LIIMs and They Look Great.

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!

How To Realign Misaligned Contours Using the "Eye-Ball" Method

Rapa Iti - NE Coast GeoTIFF Image False Color (1:10,000)

I have been working on a redo of Rapa Iti Island, using an exquisite, cloud-free GeoTIFF image, for the past month, an "on-again, off-again" project. I have completed the island's revised shorelines taking them from EVS precision to EEVS precision. That is from Enhanced Vector Shorelines using Landsat ETM+ base imagery to Extremely Enhanced Vector Shorelines using 1-meter resolution base imagery. The "zooming" capabilities of EEVS are pretty amazing. If you map it, one could zoom in to view your backyard which is in need of mowing.

Anyway, the revised Rapa Iti shoreline is finished. I still have a variety of vegetation layers to digitize, along with human ground signatures (dwellings, roads, paths, harbor features, etc). Before I tackled these challenging layers I thought I would quickly generate topographic contours. Using Global Mapper's "Generate Contours" routine, one merely needs to import the appropriate SRTM image for your area of interest, select a few options and one has contours generated in seconds. These contours, when SRTM is accurate and complete (no voids), accurately reflect the elevations of your target area. But, SRTM tiles often have little voids, which can be quickly filled using software tools (my personal favorite is SRTMFill) and in certain areas, big voids, which are difficult to reliably fill. After much thought, research and counting my money (I hate to spend money on pricey software), I decided to use a tried-and-true method "eye-ball-it". Any cartographer worth their salt cringes at this method. Too often, unscrupulous map-makers foist their finished product off as a rigorously crafted map following standard cartograph protocols, when, in fact, the map is more fiction than fact - none of which speaks kindly of the "eye-balling" method. However, since I do not have the means to obtain surveyed contour lines or modified SRTM data of my target island, I'll just "eye-ball" this portion of the project. This involves looking at the underlying land features and comparing them to accurate, reliable contours, guess-timating possible alignment of the various misaligned contour tracks (i.e., 20-meters, 40-meters, etc) and finally realigning them.

Rapa Iti - NE Coast Misaligned Contours Realigned (1:10,000)

Let's begin with Maputu Pt or the NE Coast of Rapa. Because the SRTM data was incomplete, containing a large void (no data or incomplete data), this point had contours that were spilling into the ocean.

Rapa Iti - NE Coast SRTM Base Image Misaligned Contours Realigned (1:10,000)

The above image shows the SRTM limits as a darker shade of green, when, in fact, the actual shoreline is west of the SRTM shoreline. Using the GeoTIFF image, I was able to realign the misaligned contours (see the blue contours). The method I used is "eye-balling". I looked at the shape of the easterm side of the point and beginning with the highest elevation, I realigned each contour level. The eastern side of Maputu Point appears to be quite steep, based on the GeoTIFF image and my contour realignments.

Rapa Iti - NE Coast EEVS Map with Realigned Contours Draped over SRTM Image using GM's 3D Effect (1:10,000)

Using Global Mapper's 3D Effect, I was able to see my work in a different, more revealing way. I think my "eye-balling" of the misaligned contours works quite well.

Rapa Iti - NE Coast GeoTIFF Image False Color (1:10,000)

From my GeoTIFF image to . . .

Rapa Iti - NE Coast EEVS Map Misaligned Contours Realigned (1:10,000)

Rapa Island, Maputu Point using EEVS precision (hi-res imagery). The green contours are generated from SRTM data. The blue contours are my realigned contours. They track the elevations more accurately then the SRTM based contours.

Rapa Iti - S Coast GeoTIFF Image False Color (1:10,000)

Rapa Iti - S Coast Misaligned Contours (1:10,000)

Along with the misaligned contours in the NE, another area of misaligned contours is along the southern shore. Looking at the GeoTIFF image without contours, one sees a coastline fronted by some pretty steep south facing slopes. Looking at the contours generated from the SRTM data, it is very easy to locate the problem contours. The steep slope is either poorly defined or nondefined by contours. Based on SRTM data, it appears the immediate shoreline is a very steep cliff fronting the shore. The contours do nothing toward resolving the remainder of the slope. Also the point that extends out is not defined.

Rapa Iti - S Coast EEVS Map Misaligned Contours Draped over SRTM Image with 3D Effect (1:10,000)

Looking at the contours draped over the SRTM image the reason for the misalignment is obvious. Where there should be elevation data there is none.

So I will carefully "eye-ball" the slope and assigned contours where I guess-timate they belong. You know and I know these realigned contours are nothing more than educated guesses. In the case of this map of Rapa and in consideration of the quality of the base GeoTIFF imagery, the educated guesses will ultimately lead to a good map that is useful to gather an understanding of the topography of this island. If I were to have actual contours that could be applied to this map, I could produce a high quality product useful for a wide variety of purposes. As it is, my map containing "eye-balled" contours will be a quality product useful for a variety of purposes.

Stay tuned. This project should be finished within the next few weeks. Then, you be the judge.

Enjoy!