gmt meca -Sy plots incorrectly - swapped quadrants when P and T dips are equal.

[MarshEnterprises]

Description of the problem

gmt meca: error with focal mechanism plots using the principle strain axes.

When plotting focal mechanisms with meca -Sy the tension and pressure quadrants are swapped if the dips of the T and P axes are equal.

see files below.

Full script that generated the error error_demo.gmt.txt

#!/usr/bin/env bash

gmt set MAP_FRAME_TYPE plain

gmt begin error_demo pdf

gmt basemap -B -Btblr -JM15.90/-24.45/15c -R22.15/22.5/-32.85/-32.7

# testing faulty focal mechanism (red plot) using regular input
echo -e "22.35	-32.8	5 1	360	45 1	90 0 1 180 45 1 wrong_quadrants" | gmt psmeca -Sy1+m -Gred -Vd # added -Vd for verbose output

echo -e "22.2	-32.8	5 1	360	45 1	90 0 1 180 45.1 1 correct_quadrants" | gmt psmeca -Sy1+m -Gblue

gmt end

Full error message

No error message. When using the -Vd flag the following is output:

gmt [DEBUG]: GMT_Create_Session: Terminal width = 83
gmt [DEBUG]: Obtained the ppid from parent: 173076
gmt [DEBUG]: Enter: gmtinit_new_GMT_ctrl
gmt [DEBUG]: GMT->session.SHAREDIR = /usr/local/share
gmt [DEBUG]: GMT->session.HOMEDIR = /home/ben
gmt [DEBUG]: GMT->session.USERDIR = /home/ben/.gmt [created]
gmt [DEBUG]: GMT->session.CACHEDIR = /home/ben/.gmt/cache [created]
gmt [DEBUG]: GMT: 0. Will try to find subdir=postscriptlight stem = PSL_custom_fonts suffix=.txt
gmt [DEBUG]: GMT: 1. gmt_getsharepath trying current dir
gmt [DEBUG]: GMT: 2. gmt_getsharepath trying USERDIR /home/ben/.gmt
gmt [DEBUG]: GMT: 3. gmt_getsharepath trying USERDIR subdir /home/ben/.gmt/postscriptlight
gmt [DEBUG]: GMT: 4. gmt_getsharepath trying SHAREDIR subdir /usr/local/share/postscriptlight
gmt [DEBUG]: GMT: 5. gmt_getsharepath trying SHAREDIR /usr/local/share
gmt [DEBUG]: GMT: 6. gmt_getsharepath failed
gmt [DEBUG]: Map distance calculation will be Cartesian
gmt [DEBUG]: Exit:  gmtinit_new_GMT_ctrl
gmt [DEBUG]: Enter: New_PSL_Ctrl
gmt [DEBUG]: Exit:  New_PSL_Ctrl
gmt [DEBUG]: Enter: gmt_manage_workflow
gmt [DEBUG]: GMT now running in modern mode [Session ID = 173076]
gmt [DEBUG]: Exit : gmt_manage_workflow
gmt [DEBUG]: Enter: PSL_beginsession
gmt [DEBUG]: Exit : PSL_beginsession
gmt [DEBUG]: Enter: PSL_setdefaults
gmt [DEBUG]: Exit : PSL_setdefaults
gmt [DEBUG]: Enter: gmtlib_io_init
gmt [DEBUG]: Exit : gmtlib_io_init
gmt [DEBUG]: Enter: gmt_hash_init
gmt [DEBUG]: Exit:  gmt_hash_init
gmt [DEBUG]: Enter: gmt_hash_init
gmt [DEBUG]: Exit:  gmt_hash_init
gmt [DEBUG]: Enter: gmt_reload_settings
gmt [DEBUG]: The PROJ_GEODESIC set to Vincenty
gmt [DEBUG]: gmtlib_get_graphics_item: Fig: 0 Subplot: 2 Panel: () Inset: 0
gmt [DEBUG]: Reading GMT Default parameters from file: /home/ben/.gmt/sessions/gmt_session.173076/gmt.conf
gmt [DEBUG]: Exit:  gmt_reload_settings
gmt [DEBUG]: Enter: gmtlib_plot_C_format
gmt [DEBUG]: Exit:  gmtlib_plot_C_format
gmt [DEBUG]: Enter: gmtinit_get_history
gmt [DEBUG]: gmtlib_get_graphics_item: Fig: 0 Subplot: 2 Panel: () Inset: 0
gmt [DEBUG]: Enter: gmt_hash_init
gmt [DEBUG]: Exit:  gmt_hash_init
gmt [DEBUG]: Exit:  gmtinit_get_history
gmt [DEBUG]: Initialize FFTW with 8 threads.
gmt [DEBUG]: GMT_Create_Session initialized GMT structure
gmt [DEBUG]: Loading core GMT shared library: libgmt.so
gmt [DEBUG]: Shared Library # 0 (core). Path = libgmt.so
gmt [DEBUG]: Loading GMT plugins from: /usr/local/lib/gmt/plugins
gmt [DEBUG]: Shared Library # 1 (supplements). Path = /usr/local/lib/gmt/plugins/supplements.so
gmt [DEBUG]: GMT now running in modern mode [Session ID = 173076]
gmt [INFORMATION]: Detected a classic module name (psmeca) in modern mode - please use the modern mode name meca instead.
gmt [DEBUG]: Use PS filename /home/ben/.gmt/sessions/gmt_session.173076/gmt_0.ps-
gmt [DEBUG]: gmtinit_get_current_panel: No current panel selected so not in subplot mode
gmt [DEBUG]: Modern mode: Added -R to options since history is available [22.15/22.5/-32.85/-32.7].
gmt [DEBUG]: Modern: Adding -J to options since history is available [M15.90/-24.45/15c].
gmt [DEBUG]: Revised options: -Sy1+m -Gred -Vd -R -J
meca [DEBUG]: History: Process -R
meca [DEBUG]: History: Process -J
meca [DEBUG]: Map distance calculation will be using great circle approximation with authalic auxiliary latitudes and authalic (R_2) radius = 6371007.1809 m, in meter.
meca [DEBUG]: Look for file 22.15/22.5/-32.85/-32.7 in /home/ben/.gmt
meca [DEBUG]: Look for file 22.15/22.5/-32.85/-32.7 in /home/ben/.gmt/cache
meca [DEBUG]: Look for file 22.15/22.5/-32.85/-32.7 in /home/ben/.gmt/server
meca [DEBUG]: Got regular w/e/s/n for region (22.15/22.5/-32.85/-32.7)
meca [DEBUG]: Reset MAP_ANNOT_OBLIQUE to anywhere
meca [DEBUG]: Projected values in meters: 633718 669206 -3.50879e+06 -3.49079e+06
meca [DEBUG]: Computed automatic parameters using dimension scaling: 0.909117
meca [INFORMATION]: Map scale is 2.36588 km per cm or 1:236588.
meca [DEBUG]: Running in PS mode modern
meca [DEBUG]: Use PS filename /home/ben/.gmt/sessions/gmt_session.173076/gmt_0.ps-
meca [DEBUG]: Append to hidden PS file /home/ben/.gmt/sessions/gmt_session.173076/gmt_0.ps-
meca [DEBUG]: No figure file /home/ben/.gmt/sessions/gmt_session.173076/gmt.figures - nothing to do
meca [DEBUG]: Got session name as error_demo and default graphics formats as pdf
meca [DEBUG]: Basemap order: Frame = above  Grid = below  Tick/Annot = below
meca [INFORMATION]: Linear magnitude scaling selected, normalizing by 5.
meca [DEBUG]: gmtapi_init_import: Passed family = Data Table and geometry = Point
meca [DEBUG]: gmtapi_init_import: Added 0 new sources
meca [DEBUG]: Object ID 0 : Registered Data Table Stream 7f8d0fce6aa0 as an Input resource with geometry Point [n_objects = 1]
meca [DEBUG]: gmtapi_init_import: Added stdin to registered sources
meca [DEBUG]: GMT_Init_IO: Returned first Input object ID = 0
meca [DEBUG]: gmtapi_begin_io: Input resource access is now enabled [container]
meca [DEBUG]: gmtapi_import_dataset: Passed ID = -1 and mode = 0
meca [INFORMATION]: Reading Data Table from Stream 7f8d0fce6aa0
meca [DEBUG]: Source col types: (Number,Number,Number,Number,Number,Number,Number,Number,Number,Number,Number,Number,Number,String)
meca [DEBUG]: ASCII source scanned: Numerical columns: 13, Trailing text: Y, Record type: Numerical with trailing text
meca [DEBUG]: GMT memory: Initialize 13 temporary column double arrays, each of length : 0
meca [DEBUG]: GMT memory: Initialize a temporary column char * array of length : 2097152
meca [DEBUG]: gmtapi_import_dataset processed 1 resources
meca [DEBUG]: GMT_End_IO: Input resource access is now disabled
meca [DEBUG]: GMT_End_IO: Input resource access is now disabled
meca [INFORMATION]: Number of records read: 1
meca [DEBUG]: Current size of half-baked PS file /home/ben/.gmt/sessions/gmt_session.173076/gmt_0.ps- = 23105.
meca [DEBUG]: gmtlib_garbage_collection: Destroying object: C=0 A=1 ID=0 W=Input F=Data Table M=Stream S=Used P=5580c182b610 N=(null)
meca [DEBUG]: GMTAPI_Garbage_Collection freed 1 memory objects
meca [DEBUG]: gmtlib_unregister_io: Unregistering object no 0 [n_objects = 0]
meca [DEBUG]: GMT memory: Free 13 temporary column arrays, each of length : 2097152
gmt [DEBUG]: Entering GMT_Destroy_Session
gmt [DEBUG]: gmtlib_get_graphics_item: Fig: 0 Subplot: 2 Panel: () Inset: 0

Actual outcome

T and P quadrants are swapped error_demo.pdf

Expected outcome

focal mechanism is plotted correctly.

System information

• Operating system: Ubuntu 22.04.2 LTS x86_64
• GMT version (gmt --version): GMT V6.4.0