Location Coordinates Query

Hi All,

I've been struggling with how best to define a query to get a list of unique
coordinates from a database table and my SQL skills are not good enough to
work out a good solution. The basic table structure is as follows:

CREATE TABLE [Readings Data Table] (
CY DOUBLE,
PY DOUBLE,
C1X DOUBLE, C2X DOUBLE,
P1X DOUBLE, P2X DOUBLE)

Each record in the table represents a geophysical measurement for a sensors
at the four locations (P1X,PY), (P2X,PY), (C1X,CY) and (C2X,CY). There can
be many repeat readings (ie with the same locations) and many overlapped
readings (ie which share at least one sensor location) and an example set of
data is:

CY PY C1X C2X P1X P2X
0 0 0 100 200 300
0 0 0 100 200 300
0 0 0 100 300 400
0 0 0 100 400 500
0 0 100 200 300 400
0 0 100 200 500 600
100 0 0 100 200 300

The distinct locations for this set are:

(0,0), (100,0), (200,0), (300,0), (400,0) (500,0), (600,0), (0,100),
(100,100), (200,100) and (300,100) ie there are 11 unique locations out of
the 28 (=7*4) sensor measurement locations.

My problem is to create a table with a list of just the distinct sensor
locations. I have implemented a brute-force method where I build a table by
looping through each of the four coordinate combinations to create all
possible locations and then getting just the distinct locations, but this is
quite slow with even just a moderate number of readings. Can anyone suggest
a more efficient way to get the distinct sensor locations using SQL?

Many thanks
John Paine