Hi Jianhao,
It depends what you mean by relative position.  If you mean distance, one way would be to place a marker at the map center and then measure distance between it and the marker you already have.

You can place a marker at map center with "measure center" and the "mark true" option:
<https://rbvi.ucsf.edu/chimerax/docs/user/commands/measure.html#center>

....or at specific coordinates such as 0,0,0 with "marker" and the "position" keyword to specify a point:
<https://rbvi.ucsf.edu/chimerax/docs/user/commands/marker.html#create>

Then you can select the two markers (same as atoms) with Ctrl-click, Shift-Ctrl-click and then use command "distance sel":
<https://rbvi.ucsf.edu/chimerax/docs/user/commands/distance.html>

Or regardless of whether you wanted to measure any distances, you can save the marker(s) to file and just look at the file with a text-editor to see what its coordinates are:
<https://rbvi.ucsf.edu/chimerax/docs/user/markers.html>

I hope this helps,
Elaine
-----
Elaine C. Meng, Ph.D.                       
UCSF Chimera(X) team
Department of Pharmaceutical Chemistry
University of California, San Francisco

> On May 25, 2022, at 7:54 AM, C.J. via ChimeraX-users <chimerax-users@cgl.ucsf.edu> wrote:
>
> Hi,
> I place a marker in a cryoEM map with "Volume Tracer" tool. How can I know the relative position of the marker to the origin or center of the map? Thank you!
> Best,
> Jianhao