Estimation of the position accuracy of 2 set of points with different cardinalities

Hi everyone,

A simple question:
I have 1 set of 2D location points A that I use as reference.
I have another set of location points B generated by observations.

Is there any standard method/measure to estimate a kind of position
accuracy error knowing that
- A and B dont have the same cardinality of elements e.g. B could have
more points than A?
- a point in A should be associated to only one point in B.

For the moment I created my own error measure using 3 estimations.
for a given accuracy rate (<20 meters) I compute:

- the number of discordances between A and B, which the sum of the number of omissions O (when there is no observation in B closed enough of a point in A) ,
and the number of false positive FP (when a B point has been observed but
not closed to a A point - or already taken from another observation)

- and the number of concordances between A and B, i.e. M: number of matching (when a B point is closed enought of a A point)

and then I aggregate the result = M- (O+FP) to get an indicator..

I am pretty sure there are other more traditional ways to do that.

Thanks in advance