# what does the word "transform" mean in tf?

I am new to ROS and as a result was reading about the tf package. I read this paper: http://wiki.ros.org/Papers/TePRA2013_Foote?action=AttachFile&do=view&target=TePRA2013_Foote.pdf; where the author made statements such as "...The request is the same in every case, and the programmer only needs to know the coordinate frames in which they want to operate and those relevant to the task, as long as the system knows the intermediate frames and can compute the resultant transforms.", another one is "The tf library can be separated into two different parts. The first part is disseminating transform information to the entire system. The second part of the library receives the transform information and stores it for later use".

I do not understand the context in which this word is used. My understanding of the word transform is synonymous to the word 'change'. Can you please help me understand the context in which this word is used? I do not understand what "transform information" means, and all other uses of this word in this document. Thanks for your help... this will help me better understand the package.

Originally posted by BuilderMike on ROS Answers with karma: 247 on 2017-10-05

Post score: 2

Comment by andymcevoy on 2017-10-05:
Is section 6.2 like something you're looking for?

The author is referring to coordinate transformations, the mathematical concept.

See (random internet link) Coordinate Transformations for instance.

tf is a library that makes handling such transforms in the context of robotics applications in ROS almost trivial, hence the popularity of it (and many references to it) in ROS.

From the wiki/tf2 page:

tf2 is the second generation of the transform library, which lets the user keep track of multiple coordinate frames over time. tf2 maintains the relationship between coordinate frames in a tree structure buffered in time, and lets the user transform points, vectors, etc between any two coordinate frames at any desired point in time.

And see #q270403 for a related question.

Originally posted by gvdhoorn with karma: 86574 on 2017-10-06

This answer was ACCEPTED on the original site

Post score: 4