# Capturing position data of instances using fields

I have two separate curve circles with two UV spheres instantiated on the circles at a point. I want to maintain procedural control of the location of these spheres on the circle through the angle. Here is my geometry node for this part:

I then want to capture the position data of these points/instantiated spheres to use in some mathematical operations to create a new position vector.

More specifically, I want to extract the x,y,z coordinates of the two points on the circles and then create a new position vector after performing some mathematical operations on those. Let (x1,y1,z1) be the coordinates for the sphere on the first circle, and (x2,y2,z2) be the coordinates for the sphere on the second circle. I want to create a new vector (v1,v2,v3)=(x1y2,y1x2,z1) which will then be used to plot a vector/line/instance at that location. (This is not exactly what I want, but a simpler version),

Here is my attempt:

This does not work and I am wondering if someone could tell me why, or if there is a simpler way to do this?

• a sketch would have been much more helpful than a long description... ;) Commented Dec 19, 2021 at 8:46

I might not be the easiest setup, but easier than yours ;)

I use the trim curve node and the endpoint selection node to solve this:

***UPDATE: ***

I made a nodegroup for my "orbiting sphere" which also outputs its position:

Then i instanced this nodegroup two times with different speeds and calculated a third coordinate (golden sphere) from that 2 sphere of the nodegroups:

Result: The golden sphere is always in the middle between red and blue:

a bit more fun example:

• Thanks, Chris - this is certainly a lot simpler and cleaner than the first half of my description. However, that wasn't my problem. My problem is in 'capturing' the position data of two instances on two separate circles (say), and then performing mathematical operations on those coordinates to create a third coordinate which will be the position vector for a third instance. Sorry if I have over-complicated the question - I am still learning geometry nodes (to say the least). Commented Dec 20, 2021 at 4:06
• i updated my answer Commented Dec 20, 2021 at 9:06
• Thanks, Chris - this looks great. I will implement this method into my project. (I would upvote your answer, but I don't have enough reputation) Commented Dec 20, 2021 at 9:20
• no problem. glad i could help. Commented Dec 20, 2021 at 9:50