[R-sig-Geo] Calculating areas from point data?

[Alexander Shenkin]

Hello All,

I laid out polygons based on a transect tape, and perpendicular
distances from that tape.  So, for example, one polygon could be 48m
long, at 10m, one point lies 5m to the right, at 15m another point lies
8m to the left, etc.  Connecting those points creates the polygon.

I am interested in calculating the area of those polygons.  I'm not sure
if R has a package that makes such calculations, or if I'd be better off
using something else - I'm really not sure where to turn to do this. 
Any suggestions would be greatly appreciated.

Thanks,
Allie