On https://docs.generic-mapping-tools.org/dev/cookbook/options.html#proj-codes we see
There are two conventions you may use: (a) GMT-style syntax and (b) PROJ-style syntax.
…
Oblique Mercator, 1: origin and azim -Jo|O[a|A] -Jomerc/ lon0/lat0/azim/scale|width [+v]
Seems suspicious, how could all four combinations (-Joa, -JoA, -JOa, -JOA) all
map to a single “-Jomerc”? I mean if it were that simple, then there
wouldn’t need to be four cases in the first place.
OK, my next step in my investigation was to find a working example to
test my suspicions with.
I found one on https://docs.generic-mapping-tools.org/dev/cookbook/map-projections.html#jo ,
the ‘Oblique view of Baja California’ example.
OK, I swapped out the
- -JOa120W/25N/-30/6c+v
with
- -Jomerc/120W/25N/-30/6c+v
and my suspicions were confirmed: I got a very different looking map.
That’s all I know*.
Therefore I conclude -Jo|O[a|A]
do not all just simply map to
-Jomerc
, thus options.html needs to be corrected. Probably there is
the same problem with the b and c lines there too.
(Fun fact, while looking for examples, I found there were zero -Job ones!)
$ for i in a b c
do rgrep -i -- -jo$i Downloads/gmt-6.4.0/doc_release/html/|
wc -l; done
9
0
25
(*In fact I know more. Adding -V to the original example also gave:)
coast [INFORMATION]: GMT_Parse_Options: Interval-setting -B options were reordered to appear before axis and frame -B options to ensure proper parsing.
coast [INFORMATION]: Detected a classic module name (psxy) in modern mode - please use the modern mode name plot instead.
(so maybe the example could be tightened up a little, even though
without -V one would not notice the “problem”.)