Open3D saved ply cannot be ready by pcl?

[Guptajakala]

IMPORTANT: Please use the following template to report the bug.

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Describe the bug
Open3D saved ply cannot be ready by pcl:

o3d.io.write_point_cloud(...)
pcl::io::readPLYFile(...)

Then pcl will get empty cloud

Environment (please complete the following information):

• OS: Ubuntu 16.04
• Python version: 3.6
• Open3D version: 0.9.0.0
• Is this remote workstation?: no
• How did you install Open3D?: conda

[Guptajakala]

this problem still exists.

[heethesh]

Same issue here, when converted back from ply (generated by Open3D) to pcd using the pcl_ply2pcd tool, I just see 3x3 cube of 27 points in the PCL viewer. I also don't see the ply header in the file when compared to what PCL tools generate.

[reyanshsolis]

Hi @heethesh @Guptajakala,
Thanks for finding out about this issue.

Here is what I found:

• Open3D IO (Legacy/Eigen based) only supports double. Therefore while reading the data is converted to double, and while saving x,y, z, nx, ny, nz are saved as double, while color r, g, b are converted to uchar.
• PCL PLY format does not seem to support double.
  Therefore, PLY files saved by Open3D Legacy/Eigen IO is incompatible with PCL PLY, as it lacks support for double value attributes.

However,

• The NEW Open3D Tensor IO, supports saving files in the original attribute (float -> float, double -> double). So, one may use that to save point clouds in Float, which is compatible with PCL.

Conclusion:

• PCL does not support Double attribute in PLY format (to my understanding, there might be some other way too).
• Please use the NEW Open3D Tensor IO, as is it supports various data types and custom attributes.

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PCL C++ Test Code for PLY IO:

#include <pcl/io/ply_io.h>
#include <pcl/point_types.h>

#include <iostream>

int
main(int argc, char* argv[])

{
  if (argc < 2) {
    std::cout << "Please pass the path to PLY file, as argument.";
    return 1;
  }

  const std::string path = argv[1];

  pcl::PointCloud<pcl::PointXYZ>::Ptr cloud(new pcl::PointCloud<pcl::PointXYZ>);

  if (pcl::io::loadPLYFile<pcl::PointXYZ>(path, *cloud) == -1) //* load the file
  {
    PCL_ERROR("Couldn't read file o3d_io_ply_ascii.ply \n");
    return (-1);
  }

  std::cout << "Loaded " << cloud->width * cloud->height
            << " data points from test_ply.ply with the following fields: "
            << std::endl;
  for (const auto& point : *cloud)
    std::cout << "    " << point.x << " " << point.y << " " << point.z << std::endl;

  return (0);
}

original.ply is a ply generated by PCL, with Float Points, Normals, Curvature, and UChar Colors.

Case 1: Open3D Legacy/Eigen based IO : File Generated by the following code are NOT supported by PCL.

import open3d as o3d
pcd = o3d.io.read_point_cloud("/home/rey/original.ply")
o3d.io.write_point_cloud("/home/rey/o3d_io_ply_ascii.ply", pcd, write_ascii=True, compressed=False)
o3d.io.write_point_cloud("/home/rey/o3d_io_ply_ascii_compressed.ply", pcd, write_ascii=True, compressed=False)
o3d.io.write_point_cloud("/home/rey/o3d_io_ply_bin.ply", pcd, write_ascii=False, compressed=False)
o3d.io.write_point_cloud("/home/rey/o3d_io_ply_bin_compressed.ply", pcd, write_ascii=False, compressed=True)

Case 2: Open3D New Tensor IO : File Generated by the following code are supported by PCL.

tpcd = o3d.t.io.read_point_cloud("/home/rey/original.ply")
o3d.t.io.write_point_cloud("/home/rey/o3d_tio_ply_ascii.ply", tpcd, write_ascii=True, compressed=False)
o3d.t.io.write_point_cloud("/home/rey/o3d_tio_ply_ascii_compressed.ply", tpcd, write_ascii=True, compressed=False)
o3d.t.io.write_point_cloud("/home/rey/o3d_tio_ply_bin.ply", tpcd, write_ascii=False, compressed=False)
o3d.t.io.write_point_cloud("/home/rey/o3d_tio_ply_bin_compressed.ply", tpcd, write_ascii=False, compressed=True)

Case 3: Converted to Float64/Double by Open3D and then saved by Tensor IO: File Generated by the following code are NOT supported by PCL.

tpcd_f64 = o3d.t.io.read_point_cloud("/home/rey/original.ply")

for attr in tpcd_f64.point:
    tpcd_f64.point[attr] = tpcd_f64.point[attr].to(o3d.core.float64)
    
o3d.t.io.write_point_cloud("/home/rey/o3d_tio_ply_ascii64.ply", tpcd_f64, write_ascii=True, compressed=False)
o3d.t.io.write_point_cloud("/home/rey/o3d_tio_ply_ascii_compressed64.ply", tpcd_f64, write_ascii=True, compressed=False)
o3d.t.io.write_point_cloud("/home/rey/o3d_tio_ply_bin64.ply", tpcd_f64, write_ascii=False, compressed=False)
o3d.t.io.write_point_cloud("/home/rey/o3d_tio_ply_bin_compressed64.ply", tpcd_f64, write_ascii=False, compressed=True)