# [Proj] Newbie question about cartesian coordinates.

Oscar van Vlijmen ovv at hetnet.nl
Sun Sep 10 14:19:23 EDT 2006

```> From: oon - informatika.org
> Subject: [Proj] Newbie question about cartesian coordinates.

> I want to create cartesian coordinate in Nautical Miles unit,
> which it center (0,0) on some point in Jakarta (Indonesia)
> with coordinate in WGS84: 06d11m18.00sS  106d31m36.00sE
...
>2. If the coordinate center in above, what is the point
>    (coordinate) of Medan, North Sumatera (Indonesia) with
>    coordinate in WGS84: 03d30m17.47sN 098d36m27.58sE ?
> 3. Can I use Proj to calculate the distance between two
> points above? If it can't, can you give me another
> library to calculate the distance (and do coordinate
> conversion) in WGS84 coordinate with C/C++ binding?

I cannot offer much PROJ help, but you could use the old PROJ function geod
to measure distances. Read the manual.
PROJ geod arrives (in my version) at a distance of 1386976.157 m =
748.907212 nm
A more accurate Vincenty function (not in PROJ) gives 1386976.161 m =
748.907214 nm.
Where the nautical mile is set to 1852 m.
If your coordinates have a precision of 0.01 arcseconds (= about 30 cm on
the globe), then no better accuracy in meters is needed than let's say 15
cm, so for coordinate differences as given, the PROJ geod function has an
acceptable accuracy.

```