CODEWITHSUNDEEP
pythonpython-3.xcoordinates
Archie
Archie

Reputation: 103

Transformation of Cartesian coordinates to Cylindrical coordinates

What is wrong with this, please? I would like to define Cartesian coordinate system, and then I would like to compute Cylindrical coordinate with respect to axis x.

I got an error:

    R = math.sqrt(y[i]**2 + z[i]**2)
TypeError: only size-1 arrays can be converted to Python scalars

Code:

import numpy as np
import math

XMIN =-0.15
XMAX = 0.15
YMIN = -0.1
YMAX = 0.1
ZMIN = -0.1
ZMAX = 0.1
sampling = 100

x_ = np.linspace(XMIN, XMAX, sampling)
y_ = np.linspace(YMIN, YMAX, sampling)
z_ = np.linspace(ZMIN, ZMAX, sampling)

x, y, z = np.meshgrid(x_, y_, z_, indexing='ij')

assert np.all(x[:,0,0] == x_)
assert np.all(y[0,:,0] == y_)
assert np.all(z[0,0,:] == z_)

# cylindric coordinates (R, theta, z)
R_coor = []
THETA_coor = []
Z_coor = []

for i in range(sampling-1):
    R = math.sqrt(y[i]**2 + z[i]**2)
    THETA = math.atan(y[i]/z[i])
    Z = x[i]
    R_coor.append(R)
    THETA_coor.append(THETA)
    Z_coor.append(Z)

Upvotes: 0

Views: 1275

Answers (1)

Serge Ballesta
Serge Ballesta

Reputation: 149185

Close to a typo.

In the offending line, you are using math.sqrt which can only operate on scalars. You must use the numpy version np.sqrt to operate on numpy ndarrays, or use x_, y_, z_ to have scalars.

So you should use either:

for i in range(sampling-1):
    R = math.sqrt(y_[i]**2 + z_[i]**2)
    THETA = math.atan2(y_[i], z_[i])     # always prefere atan2 to atan...
    Z = x_[i]
    R_coor.append(R)
    THETA_coor.append(THETA)
    Z_coor.append(Z)

or:

for i in range(sampling-1):
    R = np.sqrt(y[i]**2 + z[i]**2)
    THETA = np.arctan2(y[i],z[i])
    Z = x[i]
    R_coor.append(R)
    THETA_coor.append(THETA)
    Z_coor.append(Z)

Unrelated, but atan will break at pi/2 because you get an infinite quotient and can only return angle in the ]-pi/2, pi/2[ open segment, while atan2 can process the whole circle...

Upvotes: 1

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