Convert between TWD67 2D TM and WGS84 Lat/Lon coordinates

Convert between TWD67 2 degree transverse Mercator and WGS84 Lat/Lon coordinates

	TWD67 TM-2	select conversion	WGS84 Lon/Lat
x:		to WGS84		lon 經度
y:		to TWD67		lat 緯度
Show Map		format:	Dec DMS

Rationale: Taiwan's topo maps (等高線地圖) use a 2-degree transverse Mercator projection grid (二度分帶) and a local datum (虎子山經緯度座標). To meaningfully geo-reference photographs Taiwan map coordinates must be converted to the international standard WGS84 projection expressed in latitude and longitude coordinates (經緯度坐標).
Inspiration: Dan Jacobson's site.
Implementation: Python CGI of PROJ.4 with Google maps
1. convert between TWD67 and TWD97 grid with the following transform:
  A = 0.00001549
  B = 0.000006521
  X67 = X97 - 807.8 - A * X97 - B * Y97
  Y67 = Y97 + 248.6 - A * Y97 - B * X97
  X97 = X67 + 807.8 + A * X67 + B * Y67
  Y97 = Y67 - 248.6 + A * Y67 + B * X67
2. convert between TM-2 and Lat/Lon projection using proj
  ellps=GRS80 lon_0=121 x_0=250000 k=0.9999

Home (TWD67): 305041 2758840 160m (on roof)

Office (TWD67): 302800 2768212 (measured)
Should be 2768050 (25.0177) (correct on map)
instead of (y) 25.0192

http://gis.thl.ncku.edu.tw/coordtrans/coordtrans.aspx
http://140.115.123.30/QUERY/xcord.htm
http://www.ichiayi.com/gpsxy/gpsxy.php

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