opencv python Triangular mesh having coordinates

Question

I have a mesh in a stl file ( https://dl.dropboxusercontent.com/u/710615/stlMidpoint.stl )

With this code :

from stl import mesh
import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.mplot3d import Axes3D
import cv2

def unique(a):
   order = np.lexsort(a.T)
   a = a[order]
   diff = np.diff(a, axis=0)
   ui = np.ones(len(a), 'bool')
   ui[1:] = (diff != 0).any(axis=1) 

  return a[ui]

 A = np.loadtxt("vectors.txt")
 A = A[np.logical_not(A[:,2] > 0)]
 uniqA = unique(A)
 coordA = A[:,0:2]

I'm able to get the coordinates which has correspondence (I think) to the points of triangles surface. I'm trying draw the triangles without success. The points are there but not on a triangles format. I'm using polines:

img= cv2.imread('nimg.jpg')
imgMask = np.ones(img.shape[:2], dtype="uint8")*255
m_xor= np.ones(imgMask.shape, dtype="uint8") * 255

points = np.array(uniqA[:,0:2], np.int32)
print points
cv2.polylines( m_xor,[points], 1, (0,0,0))
cv2.imwrite('result.jpg', m_xor)

vectors.txt : https://dl.dropboxusercontent.com/u/710615/vectors.txt

nimg: https://dl.dropboxusercontent.com/u/710615/nimg.jpg

Wolph · Accepted Answer · 2016-03-23 17:26:02Z

3

+50

Using numpy-stl (https://github.com/WoLpH/numpy-stl) I can open, read and render the file easily:

from stl import mesh
from matplotlib import collections
from matplotlib import pyplot

# Create a figure and axes
figure, axes = pyplot.subplots()

# Read the STL file
your_mesh = mesh.Mesh.from_file('stlMidPoint.stl')

# Scale the image to the STL dimensions
axes.set_xlim(your_mesh.min_[0], your_mesh.max_[0])
axes.set_ylim(your_mesh.min_[1], your_mesh.max_[1])

# Add the polygons, but only the X and Y axis since it's 2D
axes.add_collection(collections.PolyCollection(your_mesh.vectors[:, :, :2]))

# Make sure the aspect ratio stays correct
pyplot.gca().set_aspect('equal')

# Render!
pyplot.show()

The enormous size makes it really slow however.

answered Mar 23, 2016 at 17:26

Wolph

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13 Comments

marco Over a year ago

How can I export as numpy vector and overtlay in other images?For instance, how can I apply this mesh on this image dl.dropboxusercontent.com/u/710615/La1.png , for instance. Extracting the numpy array using matplotlib I'll get the points, not the triangles.

Wolph Over a year ago

You can use figure.savefig('image.png', dpi=...) to store the image as a high-resolution image. Or use fig.canvas to access the data directly. The vector is actually already readily available through your_mesh.vectors[:, :, :2]

marco Over a year ago

Do you know a way of drawing in other context different from matplotlib ?

Wolph Over a year ago

You could use Pillow (pillow.readthedocs.org) for rendering the image. Just draw the polygons directly: pillow.readthedocs.org/en/3.1.x/reference/… But I have to say that I'm still not entirely sure what you are trying to achieve here and if this is the easiest solution for your problem.

marco Over a year ago

I need to apply this mesh to an image like this: dl.dropboxusercontent.com/u/710615/La1.png . So I need to assure the sizes are the sime, and it's better being using the same "module". I was working with opencv

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