# [Proj] Newbie question about cartesian coordinates.

oon at informatika.org oon at informatika.org
Sun Sep 10 23:56:16 EDT 2006

```Quoting Oscar van Vlijmen <ovv at hetnet.nl>:

>> 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.
>

Thanks for the information,
-----
minnie:~/proj4/bin oon\$ ./geod +ellps=WGS84 <<EOF -I +units=m
> 6d11'18"S 106d31'36"E 3d30'17.47"N 98d36'27.58"E
> EOF
-39d35'58.123"  140d35'12.901"  1386976.157
-----

For me, accuracy until 1m is no problem.

Now, i'll wait the answer for the cartesian coordinate question:
- If 6d11'18"S 106d31'36"E are center (0,0) of cartesian coordinate
(with NM units), what is the coordinate of 3d30'17.47"N 98d36'27.58"E ?
(or more precisely, with meter units)

thanks for the great software.. :)

--
regards,
Oon Arfiandwi M.
Software Engineer
Bandung, Indonesia.

```