c++ - How to visualize 2d array of doubles in vtk?

Question

I have 2d array (of size 20x30) of doubles:

double a[20*30];

How to visualize it using VTK? It is extremely difficult to find proper documentation. The closest example which I found is this, however it uses as input 3 unsigned chars which represents color. As I understand I should use vtkScalarsToColors class to somehow map scalars to colors, but I can't figure out how to put everything into single piece of code.

标签： c++vtk

Answer 1

您可能想要做的是将标量分配给表面或体积网格的点或单元。VTK 然后可以处理可视化。这在以下示例中进行了演示：ScalarBarActor。对于基本用法，请遵循标量示例。

但是，您需要自己提供要将值映射到的合适网格。从您的问题来看，“如何可视化二维数组”值的含义并不完全清楚。如果要在平面 20x30 网格中分配标量值，则需要首先创建一个vtkPolyData具有三角形或四边形单元的表面对象（类型为 ），然后使用 将值分配给网格的点surface->GetPointData()->SetScalars()，如以上示例所示.

在这种情况下方便的是vtkPlaneSource，请在此处查找相应的示例。SetXResolution()您可以分别使用或设置的网格点数SetYResolution()。（如果不清楚：vtkPlaneSource继承vtkPolyDataAlgorithm，访问底层vtkPolyData对象，使用方法GetOutput()）

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更新：为了更好的可读性，我添加了演示该过程的示例代码 - 在 python 中。

# This code has been written by normanius under the CC BY-SA 4.0 license.
# License:    https://creativecommons.org/licenses/by-sa/4.0/
# Author:     normanius: https://stackoverflow.com/users/3388962/normanius
# Date:       August 2018
# Reference:  https://stackoverflow.com/a/51754466/3388962

import vtk
import numpy as np

###########################################################
# CREATE ARRAY VALUES
###########################################################
# Just create some fancy looking values for z.
n = 100
m = 50
xmin = -1; xmax = 1
ymin = -1; ymax = 1
x = np.linspace(xmin, xmax, n)
y = np.linspace(ymin, ymax, m)
x, y = np.meshgrid(x, y)
x, y = x.flatten(), y.flatten()
z = (x+y)*np.exp(-3.0*(x**2+y**2))

###########################################################
# CREATE PLANE
###########################################################
# Create a planar mesh of quadriliterals with nxm points.
# (SetOrigin and SetPointX only required if the extent
# of the plane should be the same. For the mapping
# of the scalar values, this is not required.)
plane = vtk.vtkPlaneSource()
plane.SetResolution(n-1,m-1)
plane.SetOrigin([xmin,ymin,0])  # Lower left corner
plane.SetPoint1([xmax,ymin,0])
plane.SetPoint2([xmin,ymax,0])
plane.Update()

# Map the values to the planar mesh.
# Assumption: same index i for scalars z[i] and mesh points
nPoints = plane.GetOutput().GetNumberOfPoints()
assert(nPoints == len(z))
# VTK has its own array format. Convert the input
# array (z) to a vtkFloatArray.
scalars = vtk.vtkFloatArray()
scalars.SetNumberOfValues(nPoints)
for i in range(nPoints):
    scalars.SetValue(i, z[i])
# Assign the scalar array.
plane.GetOutput().GetPointData().SetScalars(scalars)

###########################################################
# WRITE DATA
###########################################################
writer = vtk.vtkXMLPolyDataWriter()
writer.SetFileName('output.vtp')
writer.SetInputConnection(plane.GetOutputPort())
writer.Write() # => Use for example ParaView to see scalars

###########################################################
# VISUALIZATION
###########################################################
# This is a bit annoying: ensure a proper color-lookup.
colorSeries = vtk.vtkColorSeries()
colorSeries.SetColorScheme(vtk.vtkColorSeries.BREWER_DIVERGING_SPECTRAL_10)
lut = vtk.vtkColorTransferFunction()
lut.SetColorSpaceToHSV()
nColors = colorSeries.GetNumberOfColors()
zMin = np.min(z)
zMax = np.max(z)
for i in range(0, nColors):
    color = colorSeries.GetColor(i)
    color = [c/255.0 for c in color]
    t = zMin + float(zMax - zMin)/(nColors - 1) * i
    lut.AddRGBPoint(t, color[0], color[1], color[2])

# Mapper.
mapper = vtk.vtkPolyDataMapper()
mapper.SetInputConnection(plane.GetOutputPort())
mapper.ScalarVisibilityOn()
mapper.SetScalarModeToUsePointData()
mapper.SetLookupTable(lut)
mapper.SetColorModeToMapScalars()
# Actor.
actor = vtk.vtkActor()
actor.SetMapper(mapper)
# Renderer.
renderer = vtk.vtkRenderer()
renderer.SetBackground([0.5]*3)
# Render window and interactor.
renderWindow = vtk.vtkRenderWindow()
renderWindow.SetWindowName('Demo')
renderWindow.AddRenderer(renderer)
renderer.AddActor(actor)
interactor = vtk.vtkRenderWindowInteractor()
interactor.SetRenderWindow(renderWindow)
renderWindow.Render()
interactor.Start()

结果将如下所示：