What to do with the -B0 option

[joa-quim]

This is a quick start on a discussion on -B0 initiated at #8737 and to not let it die buried in an closed issue.

Another option for -B0 could be "Do not plot frame axes" but let it plot annotations, ticks, grids, etc. I think we do not have that possibility except if we play with @100 transparencies. And even then, psscale uncovered a bug in it.

[remkos]

I thought -B0 used to mean "no frame and no annotations at all" in all other applications, like psbasemap. It would overrule the default WESN, plotting at least a frame. But I do not see it in the GMT4 manual page (https://docs.generic-mapping-tools.org/4/gmt/html/man/psbasemap.html), so it was likely an undocumented feature.

Nonetheless, it was actually an undocumented feature that I tried to employ myself with psscale recently.

But still, the syntax does show up in this current GMT6 example using (ps)coast: https://docs.generic-mapping-tools.org/latest/gallery/ex44.html#example-44

So I would like to call for a consistent use of it, i.e.,

• Support -B+n as documented, and use that in the examples, replacing -B0
• For (undocumented) backward compatibility, allow -B0 to be identical to -B+n, also in psscale.

[anbj]

If you do a grep in the doc directory, it gives 28 matches. Not all matches related to this discussion probably, but it shows that it's being used quite a bit.

$ grep -r '\-B0\s' | wc -l
28

[remkos]

Thanks, @anbj, for checking that more thoroughly than I did.
Shall we then conclude to proceed as I suggested above? That is, to replace all the -B0 with -B+n in the scripts and also support -B0 in psscale for the old dudes that have -B0 engraved in their brains.

[joa-quim]

We cannot replace -B0 by -B+n. First they don't do the same thing (though we make them do). -B0 always draws frame whilst -B+n does not. The equivalent of -B0 is -Blbrt but even that we cannot replace, because

gmt basemap -R0/1.5/0/1.7 -Jx3 -B0 -B+glightyellow -png lixo1

but if we replace -B0 by -Blrbt (or even -B+n)

gmt basemap -R0/1.5/0/1.7 -Jx3 -Blrbt -B+glightyellow -png lixo2
basemap [ERROR]: Option -B parsing failure. Correct syntax:

  -B Specify both (1) basemap frame settings and (2) axes parameters.

we would have to use the form

gmt basemap -R0/1.5/0/1.7 -Jx1i -Blrbt+glightyellow -png lixo2

BTW, gmt basemap -R0/1.5/0/1.7 -Jx1i -B+n+glightyellow -png lixo3 produces

So it seems we cannot touch it and I'll need to do the annoying trick of plotting fully transparent axes when wanting to plot a frame with tickmarks and annotations but no frame.

[anbj]

-B0 is also heavily used in the scripts in test/.

[joa-quim]

Yes, but those could be replaced by -Blrbt if we had to.

[KristofKoch]

I use -B0 quite a bit in my maps for digital usage as it gives me a thin line regardless of zoom level by the end user. Use case is overlaying GMT produced maps on a digital globe where I need to make clear where the GMT map ends without having a big fat line on higher zoom levels.

[anbj]

Me too - -B0 is very convenient.

[joa-quim]

@KristofKoch Are you sure you get a 0 thickness line with B0? When playing with it for Spilhaus projection the frame had a > 0 thickness.

[remkos]

No, it does not give 0 thickness, as gmt psbasemap -R0/1/0/1 -Jx5c -B0 will show.
It writes out 17 W to give lines with 1pt thickness.

[joa-quim]

What do you think of making these -B0 extensions:

1 -B00 means same as -B0 but with a frame with real zero line thickness (remember that 0 thickness means a line that is always thin regardless of the zooming level)

2 -B000 means no frame at all but let it plot annotations and tickmarks/grid