I have a dataset generated from running a vessel-mounted ADCP along a zig-zag pattern on a river bend (see fig1). These zig-zags were interpolated by Hydrosurveyor software to produce interpolated data points as shown in fig2, and from this interpolated dataset, I want to extract specific cross-sectional transects (marked by red lines in fig2).

I am using 'R' and not Matlab, is there any R package OR a standalone toolbox which helps in such kind of subsetting?