Hi Aishwarya,

Sorry for the late reply. Sometimes Rhino snaps to weird places, try to turn your Near snap off, maybe this helps to reduce it jumping around the canvas. I'm not sure what you mean with "the curve isn't staying constant while zooming in or out"? Sometimes when zooming in very close to curves the visibility is cut off by the Rhino display. Are you able to draw the curve just flat on the XY plane, turning your Osnaps off (forgetsnapping to the line ends, try to approximate it)? Then afterwards you can adjust the shape of the curve.

When you've drawn the interpolate curve and adjust it afterwards, it's very hard to make it touch the end points of those lines. This is because the curve wants to maintain its continuity. What you could do is add more control points to the curve, this way you constrain the curve's shape more, but it also takes more time to edit the curve to get it right. I'm attaching an image on where the command is located and some steps.

1. First draw the closed interpolate curve
2. Either insert extra control points to it (see image) Be advised, the control points added will deform the shape of the curve, but you'll be able to control the shape in a better way
3. OR instead of adding control points you add Knots (see image). Adding knots, will not deform the shape of the curve, BUT the position of the control points added will be in a different spot to accommodate for the shape of the curve to go through the knot.

Try it out and add some Control Points and after that some Knots to see the difference. I hope this explanation makes sense.

Best,

Arie