I have some vector data, where I want to visualize direction and magnitude by a cone. Basically, the direction shall be the direction of the cone and the radius of the cone shall be reflected by the magnitude.
However, when I apply a glyph filter, set it to cone and use Direction and Magnitude, the cone itself is scaled by the magnitude, not just the radius.
The cone center is set to [-0.5, 0, 0], height is 1 and radius is 0.5. As you can see, the shape stays the same (with aspect ratio 1:1) and the cones are scaled by the given scalar.
Is there any quick way to simply scale the radius?
Indeed, you cant scale “just” the radius using either Glyph filter or 3D Glyph representation.
This should be implementable using a ProgrammableFilter though.
Alright thanks! With the help of GLM4.6 I came up with some ugly solution - but it ain’t ugly if it works, right?
If someone is interested:
# This Programmable Filter creates a cone glyph at each input point.
# - Cone radius is from a scalar array named 'Magnitude'.
# - Cone orientation is from a vector array named 'Direction'.
import vtk
import math
# --- User-defined parameters ---
magnitude_array_name = 'Magnitude'
direction_array_name = 'Direction'
cone_height = 5.0
cone_res = 32
# --- User-defined parameters ---
pdi = self.GetInputDataObject(0, 0)
output = self.GetOutput()
points = pdi.GetPoints()
num_points = pdi.GetNumberOfPoints()
magnitude_array = pdi.GetPointData().GetArray(magnitude_array_name)
direction_array = pdi.GetPointData().GetArray(direction_array_name)
append_filter = vtk.vtkAppendPolyData()
# The cone's default orientation axis is along the X-axis
# But as we want to have the cone opening point into the direction, we invert here
initial_axis = (-1.0, 0.0, 0.0)
for i in range(num_points):
point = points.GetPoint(i)
radius = magnitude_array.GetValue(i)
dir_vec = direction_array.GetTuple(i)
vtk.vtkMath.Normalize(dir_vec)
cone_source = vtk.vtkConeSource()
# Shift so the tip of the cone is at the point
cone_source.SetCenter(-cone_height/2, 0, 0)
cone_source.SetHeight(cone_height)
cone_source.SetRadius(radius)
cone_source.SetResolution(cone_res)
transform = vtk.vtkTransform()
transform.PostMultiply()
dot_product = vtk.vtkMath.Dot(initial_axis, dir_vec)
# Clamp for numerical stability
if dot_product < -1.0:
dot_product = -1.0
elif dot_product > 1.0:
dot_product = 1.0
angle_rad = math.acos(dot_product)
if angle_rad > 1e-6:
rotation_axis = [0.0, 0.0, 0.0]
vtk.vtkMath.Cross(initial_axis, dir_vec, rotation_axis)
transform.RotateWXYZ(math.degrees(angle_rad), rotation_axis[0], rotation_axis[1], rotation_axis[2])
transform.Translate(point)
transform_filter = vtk.vtkTransformPolyDataFilter()
transform_filter.SetTransform(transform)
transform_filter.SetInputConnection(cone_source.GetOutputPort())
transform_filter.Update()
append_filter.AddInputConnection(transform_filter.GetOutputPort())
append_filter.Update()
output.ShallowCopy(append_filter.GetOutput())
