MAP_ANNOT_OBLIQUE 2 fails with MAP_FRAME_TYPE inside

[KristofKoch]

Description of the problem

When using

gmt set MAP_FRAME_TYPE inside
gmt set MAP_ANNOT_OBLIQUE 2

no annotation is plotted along the upper and lower plot borders. I expected longitude annotations parallel to the plot border placed on the inside of the border.

Using

gmt set MAP_FRAME_TYPE plain
gmt set MAP_ANNOT_OBLIQUE 2

everything works as expected with parallel annotations on the upper and lower border of the plot.

I expect the parallel annotations parallel to the plot border regardless of MAP_FRAME_TYPE. Combinations of bit 2 in MAP_ANNOT_OBLIQUE don't work either.

Full script that generated the error

This test script generates two identical plots except for MAP_FRAME_TYPE to highlight the problem.

#!/bin/bash

FILE1=test_map_annot_plain.ps
FILE2=test_map_annot_inside.ps

GMT_R="-R-125.1/31.6/-108.18/41.14r"
GMT_J="-JL-117.3/36.7/32.6/40/16c"

#
# ANNOTATIONS OUTSIDE (WORKS)
#

# get rid of anything that might influence the plot
rm gmt.conf
rm gmt.history

gmt set MAP_FRAME_TYPE plain
gmt set MAP_ANNOT_OBLIQUE 2

gmt psbasemap \
	${GMT_R} ${GMT_J} \
	-BWESN \
	-Bpa5f1g5 \
	> $FILE1

#
# ANNOTATIONS INSIDE (FAILS)
#

# get rid of anything that might influence the plot
rm gmt.conf
rm gmt.history

gmt set MAP_FRAME_TYPE inside
gmt set MAP_ANNOT_OBLIQUE 2

gmt psbasemap \
	${GMT_R} ${GMT_J} \
	-BWESN \
	-Bpa5f1g5 \
	> $FILE2

System information

• Operating system: 18.04.1 LTS (GNU/Linux 4.15.0 x86_64)
• Version of GMT: Version 6.0.0_68cf5ae_2019.03.08 [64-bit] [MP] [4 cores]

[joa-quim]

This (no MAP_ANNOT_OBLIQUE) gives me what you expect

psbasemap -R-125.1/31.6/-108.18/41.14r -JL-117.3/36.7/32.6/40/16c -BWESN -Bpa5f1g5 -P --MAP_FRAME_TYPE=inside

[KristofKoch]

My apologies, maybe I wasn't able to explain clear enough what I want to achieve @joa-quim. Your example gives me inside labels, but not parallel to the plot borders.

In the end I want to have:

• annotations on all four sides of the plot
• all annotations on the inside of the plot
• all annotations parallel to the plot borders.

In my understanding this should be possible with

gmt set MAP_FRAME_TYPE inside
gmt set MAP_ANNOT_OBLIQUE 34

and -BWESN in gmt psbasemap.

However, as soon as I use MAP_FRAME_TYPE inside and bit 2 in MAP_ANNOT_OBLIQUE, the annotations behave like -BWEsn is being used. Only annotations on the left and right plot border are printed instead on all four sides.

[anbj]

Related? https://gmt.soest.hawaii.edu/issues/1045

[KristofKoch]

Sounds pretty similar, @abanbj.

[joa-quim]

Ah, I see now. I guess that for the time being you would have to do something like:

psbasemap -R-125.1/31.6/-108.18/41.14r -JL-117.3/36.7/32.6/40/16c -BWESN -Bpa5f1g5 -P --MAP_FRAME_TYPE=inside --MAP_ANNOT_OBLIQUE=34 -K > lixo.ps

psbasemap -R-125.1/31.6/-108.18/41.14r -JL-117.3/36.7/32.6/40/16c -BSN -Bpa5f1g5 -P --MAP_FRAME_TYPE=inside -O >> lixo.ps

[KristofKoch]

@joa-quim maybe we talk past each other but unfortunately your example isn't exactly what I'm after. It also could have been achieved easier with a single psbasemap call:

gmt psbasemap \
    -R-125.1/31.6/-108.18/41.14r \
    -JL-117.3/36.7/32.6/40/16c \
    -BWESN \
    -Bpa5f1g5 \
    -P \
    --MAP_FRAME_TYPE=inside \
    --MAP_ANNOT_OBLIQUE=32 \
    > lixo.ps

Everything the same as your first call but --MAP_ANNOT_OBLIQUE=32 instead of 34.

The problem I have with your example is that the longitude annotations still are perpendicular to the line of longitude and not parallel to the plot border.

While this is somewhat acceptable for lower latitudes it becomes a problem at higher latitudes where the lines of longitude cross the plot border in a more and more acute angle. As the annotations are perpendicular to the lines of longitude the angle between the base line of the annotation and the plot border gets larger and larger and appear more and more slanted.

This is contrary to the docs:

This integer is a sum of 6 bit flags (most of which only are relevant for oblique projections): […] If bit 2 is set (2), then longitude annotations will be plotted horizontally. […] To set a combination of these, add up the values in parentheses. [1].

(source: MAP_ANNOT_OBLIQUE in the gmt.conf documentation)

Instead, as soon as I set bit 2, the longitude annotations just disappear. This is a bug in my eyes.

[KristofKoch]

Hi @joa-quim,

any news on this one?

All the best,
Kristof

[joa-quim]

@PaulWessel can you put this on your TOTO list?

[PaulWessel]

OK, should have time today.