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georef [2021/03/10 06:12]
allchin09 [Coordinate Conversion]
georef [2021/03/10 13:31] (current)
allchin09 [Coordinate Conversion]
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 Handy tables of parameters can be found [[https://en.wikibooks.org/wiki/PROJ.4|here]] Handy tables of parameters can be found [[https://en.wikibooks.org/wiki/PROJ.4|here]]
 +
 +=== Coordinate coversion for 1 inch to the mile millitary maps (ANG) ===
 +
  
 'Clarke Coordinates' or the 'ANG' (Australian National Grid) have the following parameters: 'Clarke Coordinates' or the 'ANG' (Australian National Grid) have the following parameters:
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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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 An explaination of parameters is as follows: An explaination of parameters is as follows:
 +=== Parameters ===
 +
 +== +proj ==
 +  * Description: Projection name
 +  * Value: tmerc
 +  * Value description:
 +    * [[https://proj.org/operations/projections/tmerc.html|Transverse mecator]]
 +    * Projection used by ANG from June 1936
 +    * Note: prior to 1936, a polyconic projection was used
 +
 +== +lat_0 ==
 +  * Description: Latitude of projection centre or true origin (TO) of projection.
 +  * Value: 34s
 +  * Value description:
 +    * The true origin of ANG is 34 degrees south
 +    * This is consistant across all 8 zones in Australia
 +
 +== +lon_0 ==
 +  * Description: Longitude of projection centre or true origin (TO) of projection. Also called central meridian (CM).
 +  * Value: 151e (for zone 8 only)
 +  * Value description:
 +    * Each zone has a different CM. ANG has 8 zones covering the width of Australia
 +    * Zone 8 covers the East of NSW
 +    * Zones and their CM values can be found in the table below
 +    * Each zone is 5 degrees wide in longitude, starting at 113d30e and ending at 153d30e
 +
 +^Zone Number  ^Western Longitude   ^Eastern Longitude ^Zone Central Meridian^
 +|1            |113d30e             |118d30e           |116de                |
 +|2            |118d30e             |123d30e           |121de                |
 +|3            |123d30e             |128d30e           |126de                |
 +|4            |128d30e             |133d30e           |131de                |
 +|5            |133d30e             |138d30e           |136de                |
 +|6            |138d30e             |143d30e           |141de                |
 +|7            |143d30e             |148d30e           |146de                |
 +|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
 +
 +== +a ==
 +  * Description: Semimajor radius of the ellipsoid axis
 +  * Value: 6378339.78
 +  * Value description:
 +    * Based on Clarke 1858 ellposid with a defined as 20,926,348 british feet
 +    * A conversion factor of 0.30479947 metres per british foot = 6,378,339.78m
 +
 +== +rf ==
 +  * Description: Inverse flattening of the ellipsoid
 +  * 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
  
-^Parameter    ^Parameter Description          ^Parameter Value  ^Value Description    ^Value Comment +== +y_0 == 
-|+proj        |Projection name                |tmerc            |Transverse Mecator   |Type of project used in ANG+  * Description: False northing 
-|+lat_0       |Latitude of projection centre  |34s              ||| +  * Value: 731518.73 
-|+lon_0       |Longitude of projection centre |151e             ||| +  Value description: 
-|+k_0         |Scale factor                   |1                ||1 is also default value| +    ANG has a false northing of 800,000 yards south of the true origin 
-|+a           |Semimajor radius of the ellipsoid axis |6378339.78||Value in british feet converted to metres| +    * Converting into metres is 800,000 / 0.91439841 = 731,518.73 metres
-|+rf          ||294.26||| +
-|+to_meter    ||0.91439841||| +
-|+x_0         |False easting                  |365759.36||| +
-|+y_0         |False northing                 |731518.73|||+
georef.1615356773.txt.gz · Last modified: 2021/03/10 06:12 by allchin09