# How do the Curve.Normal and Curve.NormalAtParameter nodes calculate the direction of normals?

**URL:** <https://forum.dynamobim.com/t/how-do-the-curve-normal-and-curve-normalatparameter-nodes-calculate-the-direction-of-normals/35157>\
**Category:** Geometry\
**Created:** [April 24, 2019, 3:10am UTC](https://forum.dynamobim.com/t/how-do-the-curve-normal-and-curve-normalatparameter-nodes-calculate-the-direction-of-normals/35157 "2019-04-24T03:10:28Z")\
**Posts on this page:** 1\
**Showing post:** 3

<div class="post-metadata">

**Author:** ![starkravingsnow](https://avatars.discourse-cdn.com/v4/letter/s/e8c25b/32.png) [@starkravingsnow](https://forum.dynamobim.com/u/starkravingsnow)\
**Post date:** [April 25, 2019, 11:34am UTC](https://forum.dynamobim.com/t/how-do-the-curve-normal-and-curve-normalatparameter-nodes-calculate-the-direction-of-normals/35157/3 "2019-04-25T11:34:33Z")

</div>

Thanks Mark. That’s a pretty useful method.

I think I’ve cracked the code (so to speak). The logic appears to follow the same methods adopted for commercial finite element programs. Below is a snippet of the local axis definition from ETABS’s analysis manual:

 ![Capture](https://us1.discourse-cdn.com/flex022/uploads/dynamobim/original/3X/a/a/aaecf679f62ad7ecc73c23986a6cbe8884197c98.jpeg)

To summarize, the local X axis is decided by the direction of the curve (start point to end point), the local Y is parallel to the Global Z axis and once the local X-Y plane is known, the curve normal direction can be found from the right-hand-thumb rule.

I’ve tested this out on a few examples and it seems to hold. I’ll leave this open in case I’m wrong and someone can advise on the correct approach.

---

_[View the full topic](https://forum.dynamobim.com/t/how-do-the-curve-normal-and-curve-normalatparameter-nodes-calculate-the-direction-of-normals/35157)._