EVS-Islands

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

I knew that this project would be challenging. I have been working on it for three-days. The mountains have some features that I still want to map. Also the coast is ringed with EVS Urban Areas that remain to be mapped. In addition, I want to delineate the farming area that encompasses the lowland between the two mountain ranges.

The map already contains 440 unique features. I have more hours to invest on this project before it is completed. My base imagery is Landsat ETM+, so some features will be roughly digitized. By the time I finish this will be a solid mapping effort.

For the curious I include the following link that gives basic information about Sadoga-shima. Hopefully, I will finish this project by next week.

I am tired and at the tail-end of a cold I caught from my students. Rest is the cure. Goodnite.

Enjoy!

Labels: island, Japan, Landsat, map, Marplot, Pacific

Posted by Mr Minton at 2/09/2007 12:12:00 AM | Permalink | Comments | links to this post

Santa Maria Island PO

The Wikipedia article about Santa Maria Island describes it as the southern most of the Azores. The island's airfield was used by the USAF during WW-II. Half of the island is relatively flat and fertile. This half is devoted to agriculture. The other half is hilly. The island was the first to be discovered and colonized by the Portugese. Today, it is a tourist destination. Not as popular as some of the larger islands, but reputed to be a great change of pace destination.

I would like to add that I have rediscovered my island mapping ways. It is nice to be going about my business, making maps of islands. This island was not overly complex. I do like my Santa Maria Island with 50m contours. It is a fine map for the intrepid island explorer. Google Earth has most of the island covered with 1-meter resolution Digital Globe imagery. I elected to not digitize from that image. I wanted to work with Landsat ETM+. It is, after all, the imagery that I began with and since I am all about rediscovering my "mapping roots", I felt Landsat ETM+ was the way to go.

Enjoy!

Labels: Atlantic, Azores, EVS, island, Landsat, map, Marplot, Portugal

Posted by Mr Minton at 2/05/2007 11:47:00 PM | Permalink | Comments | links to this post

For the past 3-days I've been lost in the world of DCW - Digital Chart of the World (aka VMAP). I know more about this grand mapping monument than I should ever know. It is based on ONC 1:1,000,000 scale military base maps that are based on some pretty old data (WW II and beyond). The ONCs were constructed for pilots to scan the earth as they are flying for identifiable features. ESRI took these maps, back in the early 1990s, and digitized them. From this data they created the Digital Chart of the World. Now let's fast forward to today.

I am currently teaching 6th graders about African geography. The region of Africa that is always a challenge is West Africa - Ivory Coast, Ghana, Togo and Benin. So I dutifully teach them and they dutifully learn all about African countries. In the process, curious soul that I am, I decided to study the available mapping of a small African country - Togo. One of my favorite mapping websites is Relief Web, a UN affiliated group that reports on people in need and helps to coordinate relief efforts, thus the name. They have a mapping library that is very interesting. So I wandered into their map library and snagged a few Togo country maps - one produced by the CIA (the bland one) and the other produced by the French government (the colorful one). The CIA map is a relatively old map, but the French product claims to be produced in 2006.

Curious soul that I am, I load the French map into Global Mapper, georectify it and digitize the road network for Togo. It didn't take long, maybe an hour. I imported this Togo road network into Marplot and compared it to the DCW Togo road network. You know the answer - it was the same road network, the DCW stuff.

And than it hit me. Almost every small scale base map found today still uses DCW layers of information. Some of these layers (elevation, rivers, etc.) will always be useful. Some of the layers, like roads, were poorly plotted on the ONCs originally and the same misplots are still being used today. Just overlay DCW roads on top of the appropriate Landsat ETM+ imagery and you will see DCW roads seldom, if ever, match the actual roads. Landsat ETM+ could be used to correct some of these transportation misplots, but it is tough to do at it's typical pixel resolution. The 1-meter resolution imagery is the ticket! (Are you listening Digital Globe?) I know it is being used to create up-to-date road maps in large cities, but it should be used to create the NEW and IMPROVED DCW. What a cartographic coup for the entreprenurial company (Are you listening Digital Globe?) that would sponser this effort!

And that was my tangent! What the heck am I messing around with Togo road networks and DCW when I want to make maps of islands. For 3-days I've been lost in DCW, Togo and off on a tangent. Oh, well, perhaps this evening I'll get back to my primary mission, island mapping, and leave my DCW / Togo tangent alone.

A word of warning - Tangents are alluring, but typically take you where you need not go. Stick to your target path. It's where you want to go.

Enjoy!

Labels: DCW, Digital Globe, ESRI, Global Mapper, Marplot, Relief Web, tangents, Togo

Posted by Mr Minton at 2/05/2007 05:49:00 AM | Permalink | Comments | links to this post