Maybe cpptraj can already do this... ?

I would like to have NAStruct local axis information for both bases and base pairs made available alongside the other pairing and step parameter information using cpptraj keywords.

The goal is to write out vector data in a pseudo-trajectory format that can be overlaid on the all atom trajectory for easy visualization.

In debug mode NAStruct can output axis information for bases (baseaxes.pdb line 316 ) and basepairs (basepairaxes.pdb line 1087) so this appears to be mostly an I/O issue.

I'm proposing something like the following
(using text adopted from El Hassan JMB 1995 Figure 1 for "base pair reference frame" and "base reference frame" and the
existing descriptors in section "35.11.54. nastruct" of Amber 22 manual)

Base pair Reference Frames: 1 frame for each base pair
[BpOrg]: x,y,z coordinates of the base pair axis origin .
[BpX-axis]: unit vector for base pair x-axis relative to BpOrg
[BpY-axis]: unit vector for base pair y-axis relative to BpOrg
[BpZ-axis]: unit vector for base pair y-axis relative to BPorg

Base Reference Frames: 1 frame for each base
[BOrg]: x,y,z coordinates of the base axis origin
[BX-axis]: unit vector for base x-axis relative to BOrg
[BY-axis]: unit vector for base y-axis relative to BOrg
[BZ-axis]: unit vector for base y-axis relative to BOrg

For comparisons

In 3DNA Base Pair axes information is reported in the "ref_frames.dat" file as follows
... 1 T-A ...
109.6665 103.8816 167.4595 # origin
0.7276 -0.6703 -0.1460 # x-axis
0.6559 0.6175 0.4341 # y-axis
-0.2008 -0.4117 0.8889 # z-axis
... 2 A-T ...
108.6866 101.8792 169.7685 # origin
0.9787 -0.2047 -0.0159 # x-axis
0.1891 0.8686 0.4581 # y-axis
-0.0799 -0.4513 0.8888 # z-axis