[Proj] Conferting from WGS84 latlong to Transverse Mercator

[Zoltan Szecsei]

On 2010-09-01 08:43, Hanlie Pretorius wrote:
> Hi,
>
> My latlong coordinates are in South Africa: 28.375E and 27.375S
>
> I'm using pyproj to convert from latlong to a Transverse Meractor PCS
> centred on 29 deg East:
>
> ---
> import pyproj
>
> pr_tm = pyproj.Proj('+proj=tmerc +lat_0=0 +lon_0=29 +k=1 +x_0=0 +y_0=0
> +ellps=WGS84 +units=m +no_defs')
>
> x_latlong = 28.375
> y_latlong = -27.375
>
> x_tm, y_tm = pr_tm(x_latlong, y_latlong)
>
> print x_tm,y_tm
> -----
>
> output:
> -----
> -61827.9202408 -3029337.78594
> -----
>
> My question is this: why is the x-coordinate in the TM PCS negative?
> It is in the eastern hemisphere, so surely it should be positive? Or
> am I missing something?
>
>    

Hi Hanlie,
Your point is west of the central meridian of Lo29.
Because you are using -ve South convention, West is also -ve, so in this 
example, the signs of the result are correct.

HTH,
Zoltan--

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Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
P.O. Box 7, Muizenberg 7950, South Africa.

65 Main Road, Muizenberg 7945
Western Cape, South Africa.

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