[Liblas-devel] Re: Stackable filters and transformers

[Howard Butler]

On May 19, 2010, at 8:36 AM, Howard Butler wrote:

> All,
> 
> A very common operation that people want to do is to filter and transform LAS data as it is being read from the file.  Common tasks that people want to do include things like:
> 
> * filter only points with the last return

Some IRC discussion with Phil and Mateusz a couple of weeks ago produced a decision that we would not implement filters and transformers in libLAS, but after some reconsideration, I think we should go ahead with implementing the concept.  My biggest reason for wanting this is that the concept of transformers will greatly simplify the reprojection machinery within libLAS.  The transformation is currently intertwined within the liblas::Reader and liblas::Writer classes, and a separate liblas::TransformI would be reusable in both the ::Reader and ::Writer cases.  

An argument against ::FilterI and ::TransformI is that they're generic concepts that don't really apply to libLAS.  A FilterI in almost all cases is not going to lead to more efficient reading of the file.  Issuing a TransformI down in the library is not going to be any more efficient than doing it up in a user's code.  But in the end, I think both of these concepts are going to lead to cleaner code -- in both internal operations of the library and user's code.

Unless I hear any serious objects, I will continue with the implementation while building up to the next release.  Expect a release plan for 1.6 soon.

Howard