I have a 3d point cloud. I used matplotlib to draw a scatterplot representing the point cloud viewed from above. The point cloud is stored as a list of coordinates in meters. The output of matplotlib.pyplot.scatter is a png image.
In addition to saving the image, I want to save the correspondence pixels <-> meters. How to do that?
Here the code I use to make my image with matplotlib. I use a dataframe to manipulate the point cloud.
colors = np.array((self.cloud["red"], self.cloud["green"], self.cloud["blue"])).T
dpi = 72
print("dpi: ",dpi)
fig = plt.figure(figsize=(18000/dpi, 18000/dpi), dpi=dpi)
ax = plt.axes(projection='3d')
ax.view_init(elev=90., azim = 0)
ax.set_snap(True)
ax.scatter(
self.cloud["x"],
self.cloud["y"],
self.cloud["z"],
marker=MarkerStyle('.', fillstyle = 'full'),
facecolors=colors / 255,
zdir="z",
#to set a point to 1 pixel we use the relation (dpi/fig.dpi) but
#the problem of the point cloud is the fact that we didn't have a point at each pixel so we increase the size of a point
#the size is empiric so need to be careful
s = (25)**2,
)
plt.axis('off')
self.set_proper_aspect_ratio(ax)
fig.tight_layout()
plt.savefig(file_name, orientation = 'portrait', transparent = True, dpi=fig.dpi)
To find this distance i use this code:
inv = ax.transData.inverted()
#center_image is in pixel
distance_x = abs(inv.transform((center_image[0],center_image[1]))[0])
distance_y = abs(inv.transform((center_image[0],center_image[1]))[1])