No color bag_to_pcd

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I answered myself this question in the PCL forum. I post the answer also here because it is a problem related to ROS and PCL.

This post has NOT been accepted by the mailing list yet. Okay, this one was tricky.

Back then, when I made the question my redaction was pretty bad. Probably that is the reason nobody could help me. Anyway, for anyone having this problem, first I will explain again the problem I had, and then the way I solved it!

Objective I had a *.bag file with point clouds in 'pcd' format and the goal was to extract each of the point clouds. In order to do this I used the bag_to_pcd node.

Procedure Once I extracted the files with ROS, I came back to PCL, and I used the "loadPCDFile" function in order to open such files. My intuition was to use a cloud with 'XYZRGB' points. This had send because by looking into the "bag_to_pcd" code, the clouds contained in the *.bag are opened as PointCloud2 and then they are transformed by using pcl_ros::transformPointCloud.

Problem The situation is that, as strange as it may sound, I could just see the depth data, but I could not see the RGB color: I was getting a message saying: "failed to find a match for field 'rgb'. This had actually no sense because the clouds had color indeed, and I could see it using rviz. Also I had already used the same procedure to convert a *bag dataset I downloaded from the CV group at TUM. So, why was this not working just for one *.bag file????

Solution To came to a solution, I tried several things, but I noticed that if I opened one of those clouds using "pcl_viewer" from the terminal, and I pressed then 5, I could see the color!!! Immediately, I went inside the pcl_viewer.cpp code, and I noticed that the clouds are declared with the format PointCloud2. My logic was to open the clouds in the same way and then transform them to 'XYZRGB' points. I tried both, the ROS and PCL functions to do so, but nothing worked!!! Then I carefully read the whole pcl_viewer.cpp, and noticed that they took a particular approach to color images!!! The trick is that the PointCloud2 is just converted into a cloud with XYZ points, then a color handler takes information directly from the cloud with format PointCloud2. Finally this handler can be used together with the 'XYZ' cloud to color it!.

The recipe 1.- Initialize two clouds: pcl::PCLPointCloud2::Ptr cloud (new pcl::PCLPointCloud2); pcl::PointCloud<pcl::pointxyz>::Ptr cloud_xyz (new pcl::PointCloud<pcl::pointxyz>);

2.- Declare a Color handler with the 'PCLPointCloud2' format: typedef pcl::visualization::PointCloudColorHandler<pcl::pclpointcloud2> ColorHandler; ColorHandler::Ptr color_handler;

3.- Open the cloud of interest using the cloud with PCLPointCloud2 format: pcl::io::loadPCDFile("name.pcd", *cloud);

4.- Use the color handler to get the RGB data: color_handler.reset (new pcl::visualization::PointCloudColorHandlerRGBField<pcl::pclpointcloud2> (cloud ... (more)