EVS-Islands

Lan-yu Tao - Landsat Image (N-51-20_2000)

Lan-yu Tao - Map

Lan-yu Tao lies off of the eastern coast of Taiwan. It is also known as Orchid Island. The island is 46 sq km in size. It's inhabitants are the Yami people (2000+). They are one of nine native groups found in Taiwan. All of these groups are Malayo-polynesian. This group migrated north from the Batanes island group.

Lan-yu Tao (22°04'N., 121°32'E.), a mountainous, steep-to, and densely-wooded island, lies about 33 miles S of Nan-liao. It is often shrouded by low-lying mist and, in winter, obscured by continuous rain. A light, with a radiobeacon, is situated on the NW point of the island. Vessels anchor in Pa-tai Wan, a small bight indenting the SW side of the island, in a depth of 18.2m, fine sand and good holding ground, with an above-water rock close off the NW entrance point of the bight bearing 270°, and a conspicuous white building, about 0.5 mile E of the same point, bearing 027°. Small vessels seeking shelter from all but E winds anchor in Tung-ch’ing Wan, a small bay on the E side of the island, in a depth of 20.1m, sand, in a position 0.3 mile offshore and midway between two villages at the head of the bay.

Caution.—Lan Yu is frequently shrouded by low-lying mist; in winter it is sometimes obscured by rain. Caution is required in approaching it, especially at night.

(SD Pub-157)

Posted by Mr Minton at 6/10/2006 09:35:00 PM | Permalink | Comments | links to this post

Comparison: SWBD and EVS - Landsat Image (1:4,000)

Comparison: SWBD and EVS - Map (1:4,000)

My EVS mapped shoreline was digitized using the Landsat image. The datum used during construction of the EVS shoreline was WGS-84. This is the same datum used during the construction of the SWBD Shoreline.

Now for the shorelines. The EVS shoreline tracks the Landsat imaged shoreline, as precisely as possible, using on-screen digitizing and considering each pixel depicts 14.3 meters of image information. The EVS Reef Shoreline layer tracks the shallows, with breaking surf, near the island's above-water shore.

SWBD uses SRTM data. When they processed their vectors, they elected to keep pixel shapes as squares. I am sure they had an option to create the shoreline vectors using an anti-alias pixels (interpolate) that would have smoothed pixel square corners. It is a "black box" function, a software engineer's mathematical solution. I consistently use this feature to prep my imagery prior to digitizing. I know for certain the shorelines do not look like the "stairs" SWBD depicts. I prefer the "smoothed" image created by the anti-alias pixel method.

Some of the SWBD vectors lineup closely with EVS shorelines, but definitely not in this case. SWBD shoreline vectors are an interesting solution, but they definitely do not replace the precision displayed by an EVS shoreline.

Posted by Mr Minton at 6/09/2006 06:31:00 AM | Permalink | Comments | links to this post

SWBD - SRTM Water Body Data

WVS - World Vector Shoreline (1:250,000)

EVS - Enhanced Vector Shoreline (Below 1:125,000)

Now that we have the three data sets identified, I will show you a map that offers an excellent display of the three aforementioned vector files.

Comparison of SWBD, WVS and EVS

The red lines are WVS map files. I believe they are out of whack due to different datums. WVS uses Nad-83 while SWBD uses WGS-84. In addition WVS was extracted from TPC (Tactical Pilotage Charts) 1:250,000 DMA produced charts. Unfortunately, these charts are based on some fairly old data (40's through the 70's).

The dark brown lines are SWBD map files. They match the Landsat base image closely. I will display their position in a zoomed image.

Comparison of SWBD, WVS and EVS - Detail

Although SWBD does track the coastline, the track is still coarse compared to the EVS map. SWBD does not attempt to depict the various motus that makeup this atoll. It tracks the shorelines.

Although SWBD is interesting and offers some highly accurate map files, they do not resolve at the same accuracy as the EVS files.

Posted by Mr Minton at 6/06/2006 10:01:00 PM | Permalink | Comments | links to this post

My output has dwindled lately due to a couple of circumstances. First circumstance - my computer system has been "fritzy". That is a technical term for a system that crashes at the worst possible moment, typically before you have saved a large amount of work. Lately, my system has been crashing and destroying my digitizing files. That is usually when I lean back in my chair and cry out in anguish. Then I take a deep breathe and start again. I think the problem is a heating problem, but that is my issue and I will solve it.

Second circumstance - the school year is ending. I have 6.5 days left and then I am out of school for the next 2.5 months. Needless to say, it is a busy time. I need the vacation to recharge my energies. Also, I need the vacation to make maps.

For the next week and a half I will map what I can and focus on the kids.

Posted by Mr Minton at 6/06/2006 10:41:00 AM | Permalink | Comments | links to this post

Kuei-shan Tao - Landsat Image (N-51-20_2000)

Kuei-shan Tao - Map

Kuei-shan Tao lies off of the eastern coast of Taiwan. It is also known as Turtle Island. A brief scan of the internet lists the island as a volcano.

Kuei-shan Tao (24°51'N., 121°57'E.), about 10 miles SSW of San-tiao Chiao, is a steep-to, precipitous volcanic island having a group of sunken pinnacle rocks about 2 miles to the SW. White vapor rises from the S shore. Sulfur, rising from the ocean floor, discolors the water to the S of the W extremity of the island.

From N and S the island resembles a tortoise with the pointed summit at its E point resembling the head and a pebble bank extending W from the W end of the island resembling the tail. A light is shown from the W side of the island.

Vessels anchor, in depths of less than 20m, sand, in a position about 0.3 mile off a small village at the head of a small bay on the NW side of the island. A prohibited anchorage, best seen on the chart, surrounds Kuei-shan Tao.

TURTLE ISLAND "This small, solitary island located about 10 kilometers off the coast of Toucheng in Yilan County has volcanic terrain that, from certain angles, looks like a turtle floating in the sea. Among the features of the island are high cliffs, steaming fumaroles, welling underwater hot springs, mountain peaks, sea-eroded caves, a lake, and unique cliff vegetation, as well as rich marine ecological resources. It is a perfect place to study volcanic terrain and the natural ecology."

Posted by Mr Minton at 6/06/2006 10:07:00 AM | Permalink | Comments | links to this post