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georef [2021/03/10 11:37]
allchin09 [Coordinate Conversion]
georef [2021/03/10 13:31] (current)
allchin09 [Coordinate Conversion]
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 | scale factor   | 1                          | | scale factor   | 1                          |
  
-Other relevant values + 
-zone 8      |+On these maps, Sydney Observatory was used as a datum for triangulation, with the following values
 +^Format ^Latitude          ^Longitude         ^ 
 +|DMS    |S 33d 51m 41.10s  |E 151d 12m 17.85s | 
 +|DD     |S 33.861417d      |E 151.204958d     | 
 + 
 +The [[http://www.ga.gov.au/ngrs/imf.jsp?site=ngrs|NGDB]] provides the following values of the observatory in different datums: 
 +^Datum  ^Latitude            ^Longitude           ^Easting       ^Northing   ^ 
 +|Clarke |S33°51' 41.107"     |E151°12' 17.993"    |420746.19     |816789.65 
 +|AGD66  |S33°51' 40.2924"    |E151°12' 12.3136"   |333809.38     |6251769.51 | 
 +|AGD84  |S33°51' 40.3241"    |E151°12' 12.2557"   |333807.91     |6251768.51 | 
 +|GDA94  |S33°51' 34.610232"  |E151°12' 16.470597" |333913.76     |6251959.42 |
  
 Note: Note:
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 |8            |148d30e             |153d30e           |151de                | |8            |148d30e             |153d30e           |151de                |
  
 +== +k_0 ==
 +  * Description: Scale factor at the central meridian
 +  * Value: 1 (default value for tmerc in PROJ)
 +  * Value description:
 +    * ANG has a scale factor (SF) of 1 at the central meridian
 +    * This means that on the CM, a measured distance on earth will equal the corresponding grid distances 
 +    * East and west of the CM, a measured distance on earth will be less than the corresponding grid distances
  
-^Parameter    ^Parameter Description          ^Parameter Value  ^Value Description    ^Value Comment              ^ +== +a == 
-|+proj        |Projection name                |tmerc            |Transverse Mecator   |Type of project used in ANG| +  * Description: Semimajor radius of the ellipsoid axis 
-|+lat_0       |Latitude of projection centre  |34s              ||| +  * Value: 6378339.78 
-|+lon_0       |Longitude of projection centre |151e             ||| +  * Value description: 
-|+k_0         |Scale factor                   |1                ||1 is also default value| +    * Based on Clarke 1858 ellposid with a defined as 20,926,348 british feet 
-|+a           |Semimajor radius of the ellipsoid axis |6378339.78||Value in british feet converted to metres| +    * A conversion factor of 0.30479947 metres per british foot = 6,378,339.78m 
-|+rf          ||294.26||| + 
-|+to_meter    |Horizontal unit value          |0.91439841|Length of a yard in metres |Yard used on coordinate grid| +== +rf == 
-|+x_0         |False easting                  |365759.36||| +  * Description: Inverse flattening of the ellipsoid 
-|+y_0         |False northing                 |731518.73|||+  * Value: 294.26 
 +  * Value description: 
 +    * Based on Clarke 1858 ellposid where the inverse flattening was defined as 294.26 
 + 
 +== +to_meter == 
 +  * Description: Horizontal unit value for output coordinates 
 +  * Value: 0.91439841 
 +  * Value description: 
 +    * The ANG coordinates are in yards 
 +    * 1 yard = 3 british feet = 0.30479947 * 3 = 0.91439841 yards per metre 
 + 
 +== +x_0 == 
 +  * Description: False easting 
 +  * Value: 365759.36 
 +  * Value description: 
 +    * ANG has a false easting of 400,000 yards west of the true origin 
 +    * Converting into metres is 400,000 / 0.91439841 = 365,759.36 metres 
 + 
 +== +y_0 == 
 +  * Description: False northing 
 +  * Value: 731518.73 
 +  * Value description: 
 +    * ANG has a false northing of 800,000 yards south of the true origin 
 +    * Converting into metres is 800,000 / 0.91439841 = 731,518.73 metres
georef.1615376274.txt.gz · Last modified: 2021/03/10 11:37 by allchin09