# How to customize the symbols on beachball？

I want to draw station symbols on the beachball, and the size and color of each station symbol will be determined by their P wave amplitude. GMT can achieve this? I learned the module polar, but I can’t write the right code.

Seems like plotting the seismic station locations on a focal mechanism is more in-depth seismology than GMT was designed to do. You may be better off using ObsPy that has all the seismology-specific plotting.

Thanks for your reply, it seems that I have to learn ObsPy.

For curiosity, can you show as an example of a beachball decorated with a station symbol?

Thanks for your interest, I’ll send a plot with symbols to indicate the stations. I would like to see the difference between the measured amplitude and the theoretical amplitude. I used a very tedious method to achieve the preliminary results.

OK, thanks (and interesting). I thought it was something simpler. To create your example plot it needs working in C side. … Still, if it happens that you know the coordinates of those symbols, a beachball is just a map projection and you could maybe add them (to the naked beachball) as custom symbols.

What you say seems to make sense, but I still don’t know how to implement it. The beachball accepts azimuths and take-off angles of a station. For my example, I first had to know the coordinate of station and then calculate the azimuths and take-off angles for these stations.
I see a polar coordinate projection in GMT, but not an equatorial polar projection, which is a specialized projection of the beachball. Draw an empty beachball, do you have time to write a line command for me.

I don’t know the solution to this. What I’m thinking is that a beachball is computed from the arrivals of the several stations. If we can know which arrival corresponds to each station than we can plot symbols for that station. The projection used in the beachballs is, I think, the Wullf projection. See the CookBook at. That figure (right side) is made with the command

``````gmt basemap -JS0/0/1.75i -Bg15 -X2.75i
``````