Add -Wo to mapproject for oblique domain in degrees

[PaulWessel]

It is useful to scripters to learn what the equivalent -R setting in degrees might be if one specifies an oblique region via -Rxmin/xmax/ymin/ymax+uunit. This PR adds that capability via -Wo which will write the w e s n numbers plus -Rstring as trailing text. Example:

gmt mapproject -R-2800/2400/-570/630+uk -Joc190/25/266/68/1:1 -Fk -C -Wo
164.589993465	210.6746652	30.1588817953	22.1514604447	-R164.589993465318/30.15888179527597/210.674665200366/22.15146044466763+r

or

Rstring=$(gmt mapproject -R-2800/2400/-570/630+uk -Joc190/25/266/68/1:1 -Fk -C -Wo -ot)

No tests are affected. Man page updated to show such an example.

[joa-quim]

Since this mixes numeric and text outputs, maybe split split this option in -Wo for numeric only and -WO for the string only (e.g. "-R....")?

[PaulWessel]

Yes, good idea. Will fix.

[maxrjones]

Is it necessary to have another one or two modifiers for this feature or could the case of an oblique region via -Rxmin/xmax/ymin/ymax+uunit be automatically detected when using -WR or -Wr as an enhancement to #5782?

[joa-quim]

Avoiding new modifiers is even better.

[PaulWessel]

Well, those are two different things though.

• -Wr|R deals with the rectangular lon/lat box that contains the oblique region. This is region you might want when pulling out a grid subset to ensure it ccovers your oblique area
• -o|O deals with the equivalent oblique specification in degrees of the box defined by projected meters/km etc

They are not the same thing, so even thought I can know internally you used +u I dont want to report one of two different things.

[PaulWessel]

Done. Example is now

gmt mapproject -R-2800/2400/-570/630+uk -Joc190/25/266/68/1:1 -WO

since -F and -C do not enter anyway (set by +u).

[anbj]

Given map, e.g.

gmt grdimage @earth_relief_10m -JS0/90/10c -R-10/20/60/70 -pdf test

I would like to find out lon/lat box that contains the oblique region (very related to #3099), hence I should use mapproject -Wr|R, per Paul's;

-Wr|R deals with the rectangular lon/lat box that contains the oblique region. This is region you might want when pulling out a grid subset to ensure it ccovers your oblique area

But not sure this works with lat/long? How would I find the box (in lat/long) containing the oblique region?

[PaulWessel]

I must not understand what you mean. Your example is not an oblique projection and the region is the one you are giving it. I.e, a grid for -10/20/60/70 should fill your map, no?

[anbj]

Sorry to be unclear. I must educate myself on this. I thought the -JS-projection was oblique…

The essence, though, in my question is; given an -R (with -JS in this case) what are the coordinates of the rectangular box that contains this ‘pie slice’ (i.e. -R[..]r). This is the wrong place to ask question; sorry.

[PaulWessel]

Hm, I see what you mean. When we say "oblique" in this context we mean a projection whose borders are not meridians and parallels. In that sense, your -JS is not oblique, while -JO etc are. Your pie slice is only "oblique" in the sense it is not a projected rectangle, but what that rectangle you talk about is depends on some other projection, no?

[anbj]

I’m in deep water here; I’m not familiar enough with projections to use correct wording. My point is maybe clearer in this post; #3099 (comment).

The ‘rectangle’ I’m talking about is basically the frame created by gmt. Thanks for answering, and sorry for misunderstanding!

PS! Your description of ‘oblique’ was very enlightening; is this the common way to describe ‘obliqueness’?

[PaulWessel]

No worries.

[anbj]

I got an epiphany this morning; my question here, as well as in #3099, has basically been how to go from a pie slice (-R) to a rectangular map (-R[..]r). After reading more in the mapproject docs I see that (among other) -Wn is my solution.

Given -JS36/90/30c -R-15/60/68/90, what -R[..]+r do I need to use?

$ gmt mapproject -JS36/90/30c -R-15/60/68/90 -Wn0/0
-1.85242110467        62.3326996594

$ gmt mapproject -JS36/90/30c -R-15/60/68/90 -Wn1/1
126   80.9626773189

I.e.: -R-1.85242110467/62.3326996594/126/80.9626773189+r

Thanks for all help!