Support lowercase types (i, u, f) when reading PCD files

[nicolaloi]

Type

• Bug fix (non-breaking change which fixes an issue): Fixes #
• New feature (non-breaking change which adds functionality). Resolves Bug in displaying pcd files with lowercase written type #6925
• Breaking change (fix or feature that would cause existing functionality to not work as expected) Resolves #

Motivation and Context

Other libraries, like PCL, support both lowercase types (i, u, f) and their uppercase "official" counterpart (I, U, F) when loading PCD files. Currently, Open3D raises an error for lowercase types when using open3d.t.io, or loads a 0.0 value when using open3d.io, without any warning/error.

Checklist:

• I have run python util/check_style.py --apply to apply Open3D code style
  to my code.
• This PR changes Open3D behavior or adds new functionality.
  • Both C++ (Doxygen) and Python (Sphinx / Google style) documentation is
    updated accordingly.
  • I have added or updated C++ and / or Python unit tests OR included test
    results (e.g. screenshots or numbers) here.
• I will follow up and update the code if CI fails.
• For fork PRs, I have selected Allow edits from maintainers.

Description

Add support for lowercase types when reading PCD files by using std::toupper(type, std::locale()).

Testing

Trying to load pc_example.zip (notice TYPE f f f instead of TYPE F F F):

# .PCD v0.7 - Point Cloud Data file format
VERSION 0.7
FIELDS x y z
SIZE 4 4 4
TYPE f f f
COUNT 1 1 1
WIDTH 4
HEIGHT 1
VIEWPOINT 0 0 0 1 0 0 0
POINTS 4
DATA ascii
1.0 2.0 3.0
1.5 2.5 3.5
0.2 4.1 -9.3
7.1 8.3 -4.7

with script:

import open3d as o3d
import numpy as np

filename = "pc_example.pcd"

print("open3d.io:")
pcd = o3d.io.read_point_cloud(filename)
print(np.asarray(pcd.points))

print("\nopen3d.t.io:")
pcd = o3d.t.io.read_point_cloud(filename)
print(pcd.point.positions.numpy())

Before

open3d.io:
[[0. 0. 0.]
 [0. 0. 0.]
 [0. 0. 0.]
 [0. 0. 0.]]

open3d.t.io:
Traceback (most recent call last):
  File "/home/nicola/Desktop/test/open3d/pcd_types/test-script.py", line 13, in <module>
    pcd = o3d.t.io.read_point_cloud(filename)
RuntimeError: [Open3D Error] (open3d::core::Dtype open3d::t::io::GetDtypeFromPCDHeaderField(char, int)) /home/nicola/Open3D-support-2D/cpp/open3d/t/io/file_format/FilePCD.cpp:115: Unsupported data type.

After

open3d.io:
[[ 1.   2.   3. ]
 [ 1.5  2.5  3.5]
 [ 0.2  4.1 -9.3]
 [ 7.1  8.3 -4.7]]

open3d.t.io:
[[ 1.   2.   3. ]
 [ 1.5  2.5  3.5]
 [ 0.2  4.1 -9.3]
 [ 7.1  8.3 -4.7]]

[ssheorey]

Thanks @nicolaloi ! Looks good!

PS: To correctly convert an Open3D Tensor to numpy, use this:

print("\nopen3d.t.io:")
pcd = o3d.t.io.read_point_cloud(filename)
print(pcd.point.positions)   # To just print directly
print(pcd.point.positions.numpy())   # convert to numpy and print