policy on publishing empty point clouds

> We currently have no policy in PCL_ROS on publishing empty PointCloud data, and some nodelets do and some don't.
> Similarly, there's no policy in PCL on whether an algorithm should return false or an error code in case its output is
> null. Good examples can be found in the filtering and segmentation frameworks.
>
>
> So:
>
> 1) if an algorithm (e.g., model segmentation) returns a null output, is this considered a failure or not? Do we:
>
> * return (false);
> * return a special code
> * write a message to screen/console
>
> Should empty PointCloud2 and pcl::PointCloud<T> be treated differently than non-empty ones?
>
> Note: this only applies to PCL.
>
> 2) should a PCL_ROS nodelet publish an empty dataset?
>
> * some people prefer this, as they need to know that the nodelet _did_ something, and returned
> * other people prefer to save bandwidth and computational resources (remember that empty PointCloud datasets need to be
> checked by every method on input! if (cloud.points.size () != 0) { .. }) and want only "valid" (non-empty) PointCloud
> datasets sent over the wire.
>
>
> Any suggestions?

>
> The "empty set" seems valid to me. Subscribers should handle it.
>
> A message saying there were no data at a particular time can be useful
> input. No message might mean the device stopped working.
>
> Often that's as easy as
>
>    for (unsigned i; i<  cloud.points.size(); ++i)
>      {
>          // handle cloud.points[i]...
>      }

> We currently have no policy in PCL_ROS on publishing empty PointCloud data, and some nodelets do and some don't.
> Similarly, there's no policy in PCL on whether an algorithm should return false or an error code in case its output is
> null. Good examples can be found in the filtering and segmentation frameworks.
>
>
> So:
>
> 1) if an algorithm (e.g., model segmentation) returns a null output, is this considered a failure or not? Do we:
>
> * return (false);
> * return a special code
> * write a message to screen/console

> Should empty PointCloud2 and pcl::PointCloud<T> be treated differently than non-empty ones?
>
> Note: this only applies to PCL.
>
> 2) should a PCL_ROS nodelet publish an empty dataset?
>
> * some people prefer this, as they need to know that the nodelet _did_ something, and returned
> * other people prefer to save bandwidth and computational resources (remember that empty PointCloud datasets need to be
> checked by every method on input! if (cloud.points.size () != 0) { .. }) and want only "valid" (non-empty) PointCloud
> datasets sent over the wire.
>
>
> Any suggestions?
>

> On 01/10/10 06:19, Radu Bogdan Rusu wrote:
>> We currently have no policy in PCL_ROS on publishing empty PointCloud data, and some nodelets do and some don't.
>> Similarly, there's no policy in PCL on whether an algorithm should return false or an error code in case its output is
>> null. Good examples can be found in the filtering and segmentation frameworks.
>>
>>
>> So:
>>
>> 1) if an algorithm (e.g., model segmentation) returns a null output, is this considered a failure or not? Do we:
>>
>> * return (false);
>> * return a special code
>> * write a message to screen/console
>
> I think that an empty point cloud could be a perfectly valid result in
> many use cases. If I try to filter all the planes in a mountain range
> from my UAV, a null result is not a failure - it's a valid result saying
> that my poor UAV has nowhere to land.
>
>> Should empty PointCloud2 and pcl::PointCloud<T>  be treated differently than non-empty ones?
>>
>> Note: this only applies to PCL.
>>
>> 2) should a PCL_ROS nodelet publish an empty dataset?
>>
>> * some people prefer this, as they need to know that the nodelet _did_ something, and returned
>> * other people prefer to save bandwidth and computational resources (remember that empty PointCloud datasets need to be
>> checked by every method on input! if (cloud.points.size () != 0) { .. }) and want only "valid" (non-empty) PointCloud
>> datasets sent over the wire.
>>
>>
>> Any suggestions?
>>
>
> Any component receiving point clouds should be able to handle an empty
> cloud.
>
> Geoff
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