# [FieldTrip] transformation matrix

Jörn M. Horschig jorn at artinis.com
Tue Apr 26 09:26:25 CEST 2016

```Hi Maris,

The transformation matrix contains the rotation, scaling (so to say, the upper-left 3x3 matrix) and other components, e.g. a translational component (the 4th column). You can think of the fourth row as a sort of a mathematical trick to end up with a square matrix, making a lot of operations easier and computationally more efficient. This 4x4 transformation matrix is actually called a projection matrix (widely used in 3D programming), and there the 4th row actually plays a big role in perspective mapping (e.g. being able to make objects farther away seem smaller).

This explanation should be roughly correct - I am not a mathematician though ;)

Best regards,

Jörn

--
Jörn M. Horschig, PhD, Software Engineer
<http://www.artinis.com/> Artinis Medical Systems  |  +31 481 350 980

From: fieldtrip-bounces at science.ru.nl [mailto:fieldtrip-bounces at science.ru.nl] On Behalf Of Maris Skujevskis
Sent: Monday, April 25, 2016 23:52
To: fieldtrip at science.ru.nl
Subject: [FieldTrip] transformation matrix

Dear Fieldtrip users,

A quick simple question (maybe it's been answered somewhere already but really I cannot find it...)

Functions like ft_read_mri and ft_volumerealign attach the field 'transform' (a 4 x 4 matrix) to the data structure ( http://www.fieldtriptoolbox.org/faq/how_to_coregister_an_anatomical_mri_with_the_gradiometer_or_electrode_positions )

My question is: what operations do each of the values in this transformation matrix correspond to?

Maris

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