Create new line: Fiducial marker to Plane

Support
1

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.

2

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.

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))

image

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).

2 Likes
3

I will try this. Thank you!

4

@lassoan

According to :point_up_2:t2: 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:

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])


![图片|455x336](upload://xatW7Xyug8DU9qB5l9hytromAvI.png)


> 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:

![图片|397x500](upload://6zoSBy6NJ1JydhrD7GTOsh83NCf.png)



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?
5 
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]
6

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

7

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.