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A NOTE ABOUT GPS COORDINATES AND GPS INBUILT COMPASS

A fundamental part of our redrawing process for the new Corregidor Maps with 5 ft contours is the collection of a series of GPS co-ordinates and matching them to the original 1932/1936 Maps. I'm particularly interested in those at old structures such as buildings and batteries that I can confirm on the old maps.

We are using the WGS84 coordinate system and UTM projection.

GPS only really use WGS84 and convert positions to other coordinate systems mathematically within the GPS itself. Projections available in this system include Geographic Projection and Universal Traverse Mercator Projection. The former uses degrees and decimal degrees; or degrees minutes and decimal minutes; or degree, minutes and seconds, as latitude and longitude. The latter uses metres east and north; and places coordinates within zones. The zone for the Philippines is 51P.

What I can say from the outset about mapping, the earth, coordinate systems and GPS is that they are a compromise. Any map distorts the earth's surface to get it to fit on the flat map. Coordinate systems are distorted based on what spheroid they use i.e. mean of elevations and depressions of the earth's surface; or the mean distance they use from the centre of the earth to the earth's surfaceProjections are distorted as they might be conical or cylindrical (most common, but there are others). Hence bearings, distances,shapes and areas can be distorted.

Most maps use the UTM projection, which gives the least distortion of curved earth surface when converted to a flat map. Therefore, maps produced using the UTM projection display shapes and angles undistorted. However, UTM maps contain some scaling particularly the further from the equator one travels north or south. What is positive about GPS, maps and the Philippines is that the country is near the equator and therefore distortion is less than for, say Japan or Canada. Corregidor is also a small island and again distortion would be minimal. So, Corregidor should have everything going for it regarding GPS and maps

GPS units contain a compass that ascertains bearings from consecutive satellite readings when the unit is moving. However, if the unit is not moving it acts like a magnetic compass. In the event that you want to use the compass on a daily basis, it should be calibrated daily. It will also need recalibrating when batteries are changed or if moving to distant locations. Double check calibration by turning the unit on; wait for satellites; press page key until the compass card is visible; press menu key once; scroll down to calibrate compass; and press entr key. Start will highlight, press entr key and rotate two full circles in the same spot. The GPS will tell you when to stop and if you are rotating too fast or slow, probably just as well because you are probably starting to feel dizzy by now. Once you get the calibrated message, press the quit key and you are done.

I'm a bit doubtful of the value of the compass for navigation as it is probably only at it's most accurate when you are moving. Stationary - mine take ages to point north and does not return to north if moved - it can be 10 degrees either way. I put it on our concrete floor to let it settle down and it went absolutely crazy. I think this was because of the steel mesh in the concrete floor. So I'm also wondering how thick the layer of bomb and shell fragments is in the soil of Corregidor. I'll bring a decent compass for January 2009.

Martyn Keen
Project Coordinator

 

           

CORREGIDOR GPS COORDINATES
(WGS84 SYSTEM)
 

    DEGREES and DECIMAL MINUTES UTM PROJECTION
    LAT LONG  METRES
EAST (mE)
METRES
NORTH (mN)
   

N (14)

E (120)

   
n/c* Waypoint degrees degrees 51 P UTM
  1000 Man Tunnel 23.072 33.881 0237382 1591642
  1942 Middleside (Old Aviary) 23.029 34.819 0239067 1591545
  B 1/5 Crockett 22.489 34.783 0238933 1590549
  Battery Cheney 22.787 34.010 0237607 1591113
  Battery Crockett 22.540 34.739 0238914 1590643
  Battery Geary 22.604 34.670 0238792 1590763
  Battery Grubbs 23.079 34.051 0237687 1591651
c Battery Hanna 23.096 33.762 0237168 1591687
  Battery Hearn 22.951 34.135 0237836 1591414
  Battery James 23.511 X34.399 0238322 1592441
  Battery Morrison 23.435 34.503 0238507 1592299
  Battery Ramsay 22.909 34.887 0239187 1591322
  Battery Smith 22.981 33.969 0237539 1591473
  Battery Smith Dirt Tunnel 22.994 33.972 0237544 1591495
  Battery Sunset 23.010 33.871 0237363 1591528
  Battery Sunset Trail 23.014 33.891 0237400 1591534
  Battery Way 23.009 34.354 0238232 1591516
  Battery Wheeler 22.661 34.263 0238060 1590875
n Cheney Hanna Bridge 22.881 34.019 0237625 1591288
n Cheney Hanna Tunnel 22.875 34.016 0237621 1591275
  Chicago 23.283 34.694 0238848 1592015
  Chicago Hill Metal Tub 23.250 34.678 0238818 1591954
  Corregidor Inn 23.202 35.266 0239873 1591855
  Crockett Steps Geary Trail 22.499 34.785 0238996 1590568
  Curved Caves 22.600 34.825 0239070 1590752
  E 1/5 Crockett 22.490 34.744 0238922 1590552
  E 1/6 Geary 22.523 34.926 0239249 1590609
  Eternal Flame 22.838 34.683 0238818 1591194
  Fiipino Memorial 23.356 35.973 0241148 1592127
  Geary Lost Mortar 22.575 34.699 0238843 1590709
  Geary Trail Big Cave 22.559 34.889 0239185 1590677
  Geary Trail Carl's Culvert 22.610 34.813 0239048 1590772
  Geary/Government Intersection 22.675 34.891 0239191 1590890
  Grubbs Beach Trail Intersection 23.181 33.852 0237332 1591843
n Hanna James Bunker 23.383 34.226 0238008 1592208
  Hospital 23.045 34.516 0238523 1591580
  Incinerator 22.856 34.920 0239246 1591223
  Jabidah Moro Marker 23.471 36.448 0242004 1592330
n James Ravine Pier 23.483 34.291 0238126 1592392
n James Ravine Water Tank 23.455 34.339 0238211 1592339
  Japanese AA Gun above North Road 23.319 35.001 0239400 1592076
  Kindley East End 23.515 36.626 0242326 1592407
  Kindley Terminal 23.467 36.343 0241817 1592324
  Kindley West End 23.473 36.242 0241634 1592337
  Lorcha Dock End 23.333 35.243 0239836 1592097
  MacArthur Café 23.291 35.275 0239893 1592019
  MacArthur Statue 23.297 35.249 0239846 1592031
  Malinta Hill Summit 23.290 35.274 0239891 1592017
  Malinta Tunnel East 23.298 35.504 0240304 1592028
  Malinta Tunnel West 23.255 35.379 0240079 1591951
  Middleside Barracks North 23.185 34.563 0238610 1591837
  Middleside Barracks South 22.996 34.731 0238910 1591485
  Navy Intercept Tunnel 23.410 36.346 0241820 1592218
  North Dock End 23.347 35.113 0239604 1592125
n Ordnance Repair Shop 23.006 34.292 0238119 1591512
  Panama Mount Tailside 23.421 36.389 0241897 1592238
  Road Culvert Government Road 22.747 34.913 0239231 1591022
  Road Culvert Government Trail 22.800 34.907 0239220 1591121
  Road Junction 43 23.383 35.594 0244168 1592183
  Rock Point Battery 23.211 33.853 0237334 1591898
  Searchlight # 2 23.273 33.870 0237365 1592012
  Searchlight # 2 Intersection 23.243 33.891 0237403 1591957
  South Dock End 22.999 35.350 0240023 1591478
  Spanish Flagpole 22.780 34.491 0238472 1591092
  Swimming Pool 22.678 34.579 0238628 1590901
  Topside Barracks East 22.899 34.581 0238638 1591308
  Topside Barracks West 22.890 34.317 0238162 1591298
  Topside Cinema 22.860 34.526 0238537 1591239
  Topside Parachute 22.841 34.606 0238618 1591201
  Wainwright Memorial 23.180 35.306 0239945 1591814
  Wall of Caves 22.533 34.904 0239211 1590628
  Way Hill Slab 23.036 34.236 0238068 1591568
n Wheeler Tunnel 22.669 34.188 0237925 1590892

* New Co-ordinates are marked "n" and corrected ones are marked "c"

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  Coordinates courtesy of Steve Kwiecinski

 

 

 

 

         

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