# Create new line: Fiducial marker to Plane
**URL:** https://discourse.slicer.org/t/create-new-line-fiducial-marker-to-plane/17572
**Category:** Support
**Created:** [May 11, 2021, 7:32pm UTC](https://discourse.slicer.org/t/create-new-line-fiducial-marker-to-plane/17572 "2021-05-11T19:32:18Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@mcastr](https://discourse.slicer.org/u/mcastr)
#### Post date: [May 11, 2021, 7:32pm UTC](https://discourse.slicer.org/t/create-new-line-fiducial-marker-to-plane/17572/1 "2021-05-11T19:32:18Z")
Operating system:Windows 10/ 64
Slicer version:4.11.20200930
Expected behavior:Unk
Actual behavior: Is there a way for a line to be projected from a point to a plane at a designated angle? For example on a skull, a plane bisecting the skull along the midline and placing a fiducial maker at the external auditory meatus, a line to be drawn from the fiducial marker at 90 degrees to the plane. Ideally, the newly drawn line would have an output of a linear measure.
---
### Author:  [@lassoan](https://discourse.slicer.org/u/lassoan)
#### Post date: [May 13, 2021, 6:08am UTC](https://discourse.slicer.org/t/create-new-line-fiducial-marker-to-plane/17572/2 "2021-05-13T06:08:32Z")
You can look up a formula on the web and adapt it to Slicer by getting inputs from markups and setting results in markups.
For example, a complete working implementation that takes a markups plane `P` and a markups line `L` as input, it takes the first control point of the line and sets its second control point to the projected position on the plane.
```python
plane = getNode('P')
line = getNode('L')
point = np.zeros(3)
planeOrigin = np.zeros(3)
planeNormal = np.zeros(3)
plane.GetOriginWorld(planeOrigin)
plane.GetNormalWorld(planeNormal)
line.GetNthControlPointPositionWorld(0, point)
distanceFromPlane = np.dot(np.subtract(point, planeOrigin), planeNormal)
line.SetNthControlPointPositionWorld(1, *(point-planeNormal*distanceFromPlane))
```
You can add an observer to the plane and line and make the line’s endpoint update automatically if the line’s starting point or the plane is adjusted (see [this example](https://slicer.readthedocs.io/en/latest/developer_guide/script_repository.html#define-edit-a-circular-region-of-interest-in-a-slice-viewer)).
---
### Author:  [@mcastr](https://discourse.slicer.org/u/mcastr)
#### Post date: [July 19, 2021, 2:44pm UTC](https://discourse.slicer.org/t/create-new-line-fiducial-marker-to-plane/17572/3 "2021-07-19T14:44:49Z")
I will try this. Thank you!
---
### Author:  [@jumbojing](https://discourse.slicer.org/u/jumbojing)
#### Post date: [December 28, 2022, 3:55pm UTC](https://discourse.slicer.org/t/create-new-line-fiducial-marker-to-plane/17572/4 "2022-12-28T15:55:21Z")
> [@lassoan](#):
>
> ```auto
> plane = getNode('P')
> line = getNode('L')
>
> point = np.zeros(3)
> planeOrigin = np.zeros(3)
> planeNormal = np.zeros(3)
> plane.GetOriginWorld(planeOrigin)
> plane.GetNormalWorld(planeNormal)
> line.GetNthControlPointPositionWorld(0, point)
> distanceFromPlane = np.dot(np.subtract(point, planeOrigin), planeNormal)
> line.SetNthControlPointPositionWorld(1, *(point-planeNormal*distanceFromPlane))
>
> ```
@lassoan
> According to 👆🏻 your code , I got the following function, which can project the point cloud to the specified plane:
根据您给的代码, 我得到了下面这个函数, 可以将点云投影到指定的平面:
```auto
def projPla(pm: XYZ,
norm: XYZ,
ps: XYZ,
# modName: str=''
) ->XYZ:
'''projPla 点射面
将点投射的平面
Args:
pm (arr): 平面上的点
norm (arr): 平面法向量
p0 (arr): 投射源点阵
Returns:
- 投射点阵
Note:
-
'''
pss = []
for p in ps:
v = np.subtract(p, pm)
p2Pla = np.dot(v, norm)
pss.append(p-norm*p2Pla)
return np.asarray(pss)
```
aa = projPla(pm, norm = np.array([0,1,0]), ps = arr[0::9])
```auto
> However, when norm=[0,0,1] or [1,0,0], an exception occurs, as shown in the following figure:
可是, 当norm = [0,0,1]或者[1,0,0]时却出现了异常如下图:
原来的点阵在投影时成了一条很窄的类似直线的形状
> The original points cloud becomes a very narrow line like shape during projection. what's wrong?
```
---
### Author:  [@jumbojing](https://discourse.slicer.org/u/jumbojing)
#### Post date: [December 28, 2022, 4:02pm UTC](https://discourse.slicer.org/t/create-new-line-fiducial-marker-to-plane/17572/5 "2022-12-28T16:02:50Z")
> [@jumbojing](#):
>
> `shape`
```auto
arr=array([[-4.93960810e+00, 7.01684875e+01, -7.48282654e+02],
[-4.71345520e+00, 7.01748428e+01, -7.49177856e+02],
[-5.63638353e+00, 7.01358185e+01, -7.44255371e+02],
[-3.81400299e+00, 7.01904144e+01, -7.51793884e+02],
[-5.54661322e+00, 7.01026306e+01, -7.41144470e+02],
[-2.60454869e+00, 7.01987686e+01, -7.54090820e+02],
[-4.79960060e+00, 7.00572891e+01, -7.37660828e+02],
[-1.85518825e+00, 7.02044754e+01, -7.55565002e+02],
[-3.73253250e+00, 7.00230179e+01, -7.35644897e+02],
[-3.09748203e-01, 7.01931992e+01, -7.56368774e+02],
[-2.07208180e+00, 6.99935226e+01, -7.34821350e+02],
[1.62125003e+00, 7.01665115e+01, -7.56150818e+02],
[-4.43809509e-01, 6.99708328e+01, -7.34618469e+02],
[3.03206897e+00, 7.01364746e+01, -7.54967896e+02],
[1.39871228e+00, 6.99509354e+01, -7.34950439e+02],
[3.92218852e+00, 7.01042480e+01, -7.52932800e+02],
[3.02136064e+00, 6.99405594e+01, -7.35936707e+02],
[4.64894152e+00, 7.00833206e+01, -7.51794067e+02],
[4.10499763e+00, 6.99445190e+01, -7.37652466e+02],
[5.83407831e+00, 7.00866241e+01, -7.53570801e+02],
[4.76213551e+00, 6.99688416e+01, -7.40820862e+02],
[7.59368277e+00, 7.00687408e+01, -7.53996399e+02],
[5.29720736e+00, 6.99932251e+01, -7.43844666e+02],
[9.85618973e+00, 7.00391693e+01, -7.53905396e+02],
[6.18222475e+00, 6.99629135e+01, -7.41989746e+02],
[1.11831875e+01, 7.00229416e+01, -7.53960144e+02],
[7.05674744e+00, 6.99254150e+01, -7.39423584e+02],
[1.32680683e+01, 6.99938354e+01, -7.53695557e+02],
[8.51561928e+00, 6.98925323e+01, -7.38023621e+02],
[1.47315636e+01, 6.99666748e+01, -7.52856750e+02],
[1.01131620e+01, 6.98743820e+01, -7.38224731e+02],
[1.53441133e+01, 6.99283218e+01, -7.49886108e+02],
[1.16029158e+01, 6.98721085e+01, -7.39833740e+02],
[1.46470222e+01, 6.99058533e+01, -7.46848816e+02],
[1.25617809e+01, 6.98832474e+01, -7.42093201e+02],
[1.36347218e+01, 6.98939819e+01, -7.44453247e+02]]) # arr = arr[0::9]
```
---
### Author:  [@esomjai](https://discourse.slicer.org/u/esomjai)
#### Post date: [March 20, 2023, 12:15pm UTC](https://discourse.slicer.org/t/create-new-line-fiducial-marker-to-plane/17572/6 "2023-03-20T12:15:00Z")
> [@lassoan](#):
>
> ```auto
> plane = getNode('P')
> line = getNode('L')
>
> point = np.zeros(3)
> planeOrigin = np.zeros(3)
> planeNormal = np.zeros(3)
> plane.GetOriginWorld(planeOrigin)
> plane.GetNormalWorld(planeNormal)
> line.GetNthControlPointPositionWorld(0, point)
> distanceFromPlane = np.dot(np.subtract(point, planeOrigin), planeNormal)
> line.SetNthControlPointPositionWorld(1, *(point-planeNormal*distanceFromPlane))
>
> ```
I am experiencing issues with applying this code in Slicer 5.2.2.
I am also quite new to the program, therefore the language. I am currently working on facial DICOM files and their landmarking. I established a frankfort horizontal plane as a reference for further measurements. I am struggling to project a specified point orthogonally to the plane - tried to compute coordinated with MatLab but failed (not even intersecting the plane). I will also need to establish the point(s) where different lines intersect the plane (not in 90°) for angle measurements as well. Can this be done using visual modules?
Many thanks,
Eszter
---
### Author:  [@lassoan](https://discourse.slicer.org/u/lassoan)
#### Post date: [March 20, 2023, 3:05pm UTC](https://discourse.slicer.org/t/create-new-line-fiducial-marker-to-plane/17572/7 "2023-03-20T15:05:05Z")
You need to have a plane node by the name `P` and a line node by the name `L` in the scene. The script updates the second point of the line to make the line orthogonal to the plane. I’ve just tried the code snippet in Slicer-5.2.2 and it worked perfectly.