[Manifold-l] Custom datums

[adamw at manifold.net]

> Fiji Geodetic Datum 1986 (from WGS84)
> 
>  Ox: -1.37101925914775"
>  Oy: 0.841968640179647"
>  Oz: 4.718005596536956"
>  dx: 35.17277931989845m
>  dy: -136.5712601696053m
>  dz: 36.96429263506973m
>  m: 1.537002362494988ppm

>  <xml>
>  <datum>
>  <name>Fiji Geodetic Datum 1986</name>
>  <ellipsoid>WGS72</ellipsoid>
>  <centerX>35.17277931989845 </centerX>
>  <centerY>-136.5712601696053 </centerY>
>  <centerZ>36.96429263506973m </centerZ>
>  <rotationX>-1.37101925914775</rotationX>
>  <rotationY>0.841968640179647</rotationY>
>  <rotationZ>4.718005596536956</rotationZ>
>  </datum>
>  </xml>

The value of <centerZ> should not include the letter "m".

The values of <rotationX>, <rotationY> and <rotationZ> are in degrees so if Ox, Oy, Oz are in minutes, you should divide them by 60.

> Also understand Manifold doesn't consider the 7th (scale)
> parameter in the transformation (so left it out). Is this correct,
> & what affect does it have on accuracy?

Yes, this is correct. The error should not exceed 10 meters (the radius of the Earth * m * 10e-6).

> Fiji Map Grid, FMG:
> 
>  Projection: Transverse Mercator
>  Datum: Fiji Geodetic Datum 1986
>  Spheroid: WGS72
>  Longitude: 178d45'00"E
>  Latitude: 17d00'00"S
>  Scale Factor: 0.9998548
>  False Easting: 2,000,000
>  False Northing: 4,000,000

>  <xml>
>  <preset>
>  <name>Fiji Map Grid</name>
>  <category>National Grids*Fiji</category>
>  <system>Transverse Mercator</system>
>  <datum>Fiji Geodetic Datum 1986</datum>
>  <centerLat>17</centerLat>
>  <centerLon>178.75</centerLon>
>  <scaleX>0.9998548</scaleX>
>  <scaleY>0.9998548</scaleY>
>  <falseEasting>2000000</falseEasting>
>  <falseNorthing>4000000</falseNorthing>
>  </preset>
>  </xml>

The value of <centerLat> should be -17 (southern latitude).

--
Adam Wachowski
Manifold Development Team