Writing Point Cloud data to PCD files

In this tutorial we will learn how to write point cloud data to a PCD file.

The code

First, create a file called, let’s say, pcd_write.cpp in your favorite editor, and place the following code inside it:

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#include <iostream>
#include <pcl/io/pcd_io.h>
#include <pcl/point_types.h>

int
  main (int argc, char** argv)
{
  pcl::PointCloud<pcl::PointXYZ> cloud;

  // Fill in the cloud data
  cloud.width    = 5;
  cloud.height   = 1;
  cloud.is_dense = false;
  cloud.points.resize (cloud.width * cloud.height);

  for (size_t i = 0; i < cloud.points.size (); ++i)
  {
    cloud.points[i].x = 1024 * rand () / (RAND_MAX + 1.0f);
    cloud.points[i].y = 1024 * rand () / (RAND_MAX + 1.0f);
    cloud.points[i].z = 1024 * rand () / (RAND_MAX + 1.0f);
  }

  pcl::io::savePCDFileASCII ("test_pcd.pcd", cloud);
  std::cerr << "Saved " << cloud.points.size () << " data points to test_pcd.pcd." << std::endl;

  for (size_t i = 0; i < cloud.points.size (); ++i)
    std::cerr << "    " << cloud.points[i].x << " " << cloud.points[i].y << " " << cloud.points[i].z << std::endl;

  return (0);
}

The explanation

Now, let’s break down the code piece by piece.

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

pcl/io/pcd_io.h is the header that contains the definitions for PCD I/O operations, and pcl/point_types.h contains definitions for several PointT type structures (pcl::PointXYZ in our case).

  pcl::PointCloud<pcl::PointXYZ> cloud;

describes the templated PointCloud structure that we will create. The type of each point is set to pcl::PointXYZ, which is:

// \brief A point structure representing Euclidean xyz coordinates.
struct PointXYZ
{
  float x;
  float y;
  float z;
};

The lines:

  // Fill in the cloud data
  cloud.width    = 5;
  cloud.height   = 1;
  cloud.is_dense = false;
  cloud.points.resize (cloud.width * cloud.height);

  for (size_t i = 0; i < cloud.points.size (); ++i)
  {
    cloud.points[i].x = 1024 * rand () / (RAND_MAX + 1.0f);
    cloud.points[i].y = 1024 * rand () / (RAND_MAX + 1.0f);
    cloud.points[i].z = 1024 * rand () / (RAND_MAX + 1.0f);
  }

fill in the PointCloud structure with random point values, and set the appropriate parameters (width, height, is_dense).

Then:

  pcl::io::savePCDFileASCII ("test_pcd.pcd", cloud);

saves the PointCloud data to disk into a file called test_pcd.pcd

Finally:

  std::cerr << "Saved " << cloud.points.size () << " data points to test_pcd.pcd." << std::endl;

  for (size_t i = 0; i < cloud.points.size (); ++i)
    std::cerr << "    " << cloud.points[i].x << " " << cloud.points[i].y << " " << cloud.points[i].z << std::endl;

is used to show the data that was generated.

Compiling and running the program

Add the following lines to your CMakeLists.txt file:

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cmake_minimum_required(VERSION 2.8 FATAL_ERROR)

project(pcd_write)

find_package(PCL 1.2 REQUIRED)

include_directories(${PCL_INCLUDE_DIRS})
link_directories(${PCL_LIBRARY_DIRS})
add_definitions(${PCL_DEFINITIONS})

add_executable (pcd_write pcd_write.cpp)
target_link_libraries (pcd_write ${PCL_LIBRARIES})

After you have made the executable, you can run it. Simply do:

$ ./pcd_write

You will see something similar to:

Saved 5 data points to test_pcd.pcd.
  0.352222 -0.151883 -0.106395
  -0.397406 -0.473106 0.292602
  -0.731898 0.667105 0.441304
  -0.734766 0.854581 -0.0361733
  -0.4607 -0.277468 -0.916762

You can check the content of the file test_pcd.pcd, using:

$ cat test_pcd.pcd
# .PCD v.5 - Point Cloud Data file format
FIELDS x y z
SIZE 4 4 4
TYPE F F F
WIDTH 5
HEIGHT 1
POINTS 5
DATA ascii
0.35222 -0.15188 -0.1064
-0.39741 -0.47311 0.2926
-0.7319 0.6671 0.4413
-0.73477 0.85458 -0.036173
-0.4607 -0.27747 -0.91676