[Proj] Local Projection Selection

[Patrick Mézard]

Hello,
I have a function performing distance calculations between points 
defined in WGS-84 and perhaps some angular computations too. The input 
dataset is always restricted to an area of at most 20km around a center 
point, and usually 10km. The area center is unspecified, but extreme 
cases (earth poles) are excluded.

For every function call, I would like to reproject the input dataset 
into a euclidian space where I could perform metric computations. 
Accuracy is important but not critical (I could cope with offsets of 
2/3m), computation speed is important too since the function is 
implemented on mobile devices where floating-point computations are 
rather slow.

Could you give me advices to select a projection in PROJ.4 I could 
configure with a center point (x,y), matching the constraints above.

Thank you for any hint.

Patrick Mézard