# How to define a point (visible and snapable one)?

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I want to define a point (U in the following drawing) and use it as a reflection point to find the reflection of vertices of a triangle regarding this point.

I know there is "point" command and I can define a point with this command.

Upon defining the point, I can't see it in the monitor and I can't snap it to draw the line.

How can I make it visible and apply snap to point?

My main issue is as follows: In the triangle ABC and point U are given, points A', B' and C' are reflection of points A,B and C according to point U. What is the easiest way to obtain points A', B; and C' and draw the polygon?

I do as follow although might not be a smart way:

In order to find the reflection point, I want to draw a circle with center located in this point (U), and radius is known (AU, Bu and CU), then draw the ray from A, B and C passing through point U and then trim the ray. If you have better solution for finding the reflex, please let me know.

Reflection is same as mirror but my object is an imaginary point (A, B and C) and I don't know if I can apply the mirror command in this case.

reflection.dwg

Edited by khoshravan
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How can I make it visible and apply snap to point?

b) Node OSnap

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. . . .

What is the easiest way to obtain points A', B; and C' and draw the polygon?

. . . .

I think if you placed points at A, B, C, and U then you could just rotate A, B, and C 180 degrees around U. The ROTATE command has a COPY option to keep the original locations intact.

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Thanks. It looks that size of point marker (ddptype) has two options, relative to screen and absolute. Thanks again.

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I think if you placed points at A, B, C, and U then you could just rotate A, B, and C 180 degrees around U. The ROTATE command has a COPY option to keep the original locations intact.

Very clever point:thumbsup:. I have focused on the problem solving and was totally unaware of this simple point. Thanks a lot.

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