Let -Jp|P optionally set what angles"w/e" really are

doc/rst/source/explain_-J.rst_

@@ -275,7 +275,7 @@ respectively):
 
 .. _-Jp_full:
 
-    **-Jp**\|\ **P**\ *scale*\|\ *width*\ [**+a**]\ [**+f**\ [**e**\|\ **p**\|\ *radius*]]\
+    **-Jp**\|\ **P**\ *scale*\|\ *width*\ [**+a**]\ [**+f**\ [**e**\|\ **p**\|\ *radius*]]\ [**+k**\ *kind*]\
     [**+r**\ *offset*][**+t**\ *origin*][**+z**\ [**p**\|\ *radius*]]] (Polar coordinates (*theta*, *r*))
 
     Give *scale* (with **-Jp**; in :ref:`plot-units <plt-units>`/r-unit) or *width* (with **-JP**; in
@@ -286,6 +286,7 @@ respectively):
     - **+f** to flip the radial direction to point inwards, and append **e** to indicate that *r* represents
       *elevations* in degrees (requires *south* >= 0 and *north* <= 90), **p** to select current planetary radius
       (determined by :term:`PROJ_ELLIPSOID`) as maximum radius [*north*], or *radius* to specify a custom radius.
+    - **+k** sets the annotation *kind* to be longitudes (*x*) or latitudes (*y*) [Default is unspecified angles].
     - **+r**\ *offset* to include a radial offset in measurement units [default is **0**].
     - **+t**\ *origin* in degrees so that this angular value is aligned with the positive *x*-axis (or the azimuth to
       be aligned with the positive *y*-axis if **+a**) [default is **0**].

doc/rst/source/proj-codes.rst_

@@ -102,7 +102,7 @@
    * - :ref:`Polar [azimuthal] <-Jp>`  (:math:`\theta, r`) (or cylindrical)
      - **-Jp**\|\ **P**
      - **-Jpolar/**
-     - *scale*\|\ *width*\ [**+a**]\ [**+f**\ [**e**\|\ **p**\|\ *radius*]]\
+     - *scale*\|\ *width*\ [**+a**]\ [**+f**\ [**e**\|\ **p**\|\ *radius*]]\ [**+k**\ *kind*]\
        [**+r**\ *offset*][**+t**\ *origin*][**+z**\ [**p**\|\ *radius*]]
    * - :ref:`(American) polyconic <-Jpoly>` 
      - **-Jpoly**\|\ **Poly**

src/gmt_init.c

@@ -5026,10 +5026,10 @@ GMT_LOCAL bool gmtinit_parse_J_option (struct GMT_CTRL *GMT, char *args_in) {
 			gmt_set_column_type (GMT, GMT_IN, GMT_Y, GMT_IS_FLOAT);
 			GMT->current.proj.got_azimuths = GMT->current.proj.got_elevations = false;
 			GMT->current.proj.z_down = GMT_ZDOWN_R;
-			if ((d = gmt_first_modifier (GMT, args, "afrtz"))) {	/* Process all modifiers */
+			if ((d = gmt_first_modifier (GMT, args, "afkrtz"))) {	/* Process all modifiers */
 				unsigned int pos = 0, uerr = 0;
 				char word[GMT_LEN32] = {""};
-				while (gmt_getmodopt (GMT, 'J', d, "afrtz", &pos, word, &uerr) && uerr == 0) {
+				while (gmt_getmodopt (GMT, 'J', d, "afkrtz", &pos, word, &uerr) && uerr == 0) {
 					switch (word[0]) {
 						case 'a':	/* Using azimuths instead of directions */
 							GMT->current.proj.got_azimuths = true;
@@ -5050,6 +5050,16 @@ GMT_LOCAL bool gmtinit_parse_J_option (struct GMT_CTRL *GMT, char *args_in) {
 									break;
 							}
 							break;
+						case 'k':	/* Gave optional +k to indicate angles are longitude (x) or latitude (y) [Just great circle angles] */
+							switch (word[1]) {
+								case 'x':	GMT->current.proj.angle_kind = GMT_IS_LON;	break;
+								case 'y':	GMT->current.proj.angle_kind = GMT_IS_LAT;	break;
+								default:
+									GMT_Report (GMT->parent, GMT_MSG_ERROR, "Polar projection: +%s not a valid argument\n", word);
+									error++;
+									break;
+							}
+							break;
 						case 'r':	/* Gave optional +r for a nonzero radial offset [0] */
 							GMT->current.proj.radial_offset = gmt_M_to_inch (GMT, &word[1]);
 							break;
@@ -5083,10 +5093,6 @@ GMT_LOCAL bool gmtinit_parse_J_option (struct GMT_CTRL *GMT, char *args_in) {
 				if (uerr) return (GMT_PARSE_ERROR);
 				GMT->current.proj.pars[0] = gmt_M_to_inch (GMT, args);
 				if (d) d[0] = '+';	/* Restore modifiers */
-//				if (GMT->current.proj.z_down && GMT->current.proj.flip) {
-//					GMT_Report (GMT->parent, GMT_MSG_ERROR, "Polar projection: Cannot select both +f and +z modifiers\n");
-//					error++;
-//				}
 			}
 			else {	/* No modifiers, so look for deprecated syntax such as -Jp|p[a|A], slash-separated scale|width and angular offset, and trailing r or z codes */
 				if (args[0] == 'a' || args[0] == 'A') {	/* Using azimuths instead of directions */
@@ -5113,6 +5119,10 @@ GMT_LOCAL bool gmtinit_parse_J_option (struct GMT_CTRL *GMT, char *args_in) {
 				else
 					error++;
 			}
+			if (GMT->current.proj.got_azimuths && GMT->current.proj.angle_kind) {
+				GMT_Report (GMT->parent, GMT_MSG_ERROR, "Polar projection: Cannot select both +a and +k\n");
+				error++;
+			}
 			if (GMT->current.proj.got_azimuths) GMT->current.proj.pars[1] = -GMT->current.proj.pars[1];	/* Because azimuths go clockwise */
 			break;
 
@@ -7133,14 +7143,17 @@ void gmtlib_explain_options (struct GMT_CTRL *GMT, char *options) {
 			gmt_message (GMT, "\t       Upper-case A|B|C removes enforcement of a northern hemisphere pole.\n");
 			gmt_message (GMT, "\t       Append +v to make the oblique Equator the y-axis [x-axis].\n");
 
-			gmt_message (GMT, "\t   -Jp|P<scale>|<width>[+a][+f[e|p|<radius>]][+r<offset>][+t<origin>][+z[p|<radius>]] (Polar (theta,radius))\n");
+			gmt_message (GMT, "\t   -Jp|P<scale>|<width>[+a][+f[e|p|<radius>]][+k<kind>][+r<offset>][+t<origin>][+z[p|<radius>]] (Polar (theta,radius))\n");
 			gmt_message (GMT, "\t     Linear scaling for polar coordinates.  Give scale in %s/units.\n",
 			             GMT->session.unit_name[GMT->current.setting.proj_length_unit]);
 			gmt_message (GMT, "\t     Append +a to use azimuths (CW from North) instead of directions (CCW from East) [Default].\n");
 			gmt_message (GMT, "\t     Append +f to flip radial direction so that south is on the outside and north is at the center.\n");
 			gmt_message (GMT, "\t       Append e to indicate data are elevations in degrees (s/n must be in 0-90 range).\n");
 			gmt_message (GMT, "\t       Append p to set r = current planetary radius to be the center.\n");
 			gmt_message (GMT, "\t       Append <radius> to indicate the radius at the center.\n");
+			gmt_message (GMT, "\t     Append +k to specify angular kind [angles].\n");
+			gmt_message (GMT, "\t       Append x to indicate angles should be formatted as longitude.\n");
+			gmt_message (GMT, "\t       Append y to indicate angles should be formatted as latitude.\n");
 			gmt_message (GMT, "\t     Append +r to offset the radial values [0].\n");
 			gmt_message (GMT, "\t     Append +t to set <origin> value for angles or azimuths [0].\n");
 			gmt_message (GMT, "\t     Append +z to annotate depths rather than radius [Default]. Alternatively, if you provided depths\n");
@@ -7257,7 +7270,7 @@ void gmtlib_explain_options (struct GMT_CTRL *GMT, char *options) {
 
 			gmt_message (GMT, "\t   -Jy|Y[<lon0>/[<lat0>/]]<scl>|<width> (Cylindrical Equal-area)\n");
 
-			gmt_message (GMT, "\t   -Jp|P<scl>|<width>[+a][+f[e|p|<radius>]][+o<offset>][+r<origin][+z[p|<radius>]] (Polar [azimuth] (theta,radius))\n");
+			gmt_message (GMT, "\t   -Jp|P<scl>|<width>[+a][+f[e|p|<radius>]][+k<kind>][+r<offset>][+t<origin][+z[p|<radius>]] (Polar [azimuth] (theta,radius))\n");
 
 			gmt_message (GMT, "\t   -Jx|X<x-scl>|<width>[d|l|p<power>|t|T][/<y-scl>|<height>[d|l|p<power>|t|T]] (Linear, log, and power projections)\n");
 			gmt_message (GMT, "\t   (See basemap for more details on projection syntax)\n");

src/gmt_map.c

@@ -2794,6 +2794,10 @@ GMT_LOCAL int gmtmap_init_polar (struct GMT_CTRL *GMT, bool *search) {
 
 	*search = false;
 	gmtproj_vpolar (GMT, GMT->current.proj.pars[1]);
+	if (GMT->current.proj.angle_kind == GMT_IS_LAT && (GMT->common.R.wesn[XLO] < -90.0 || GMT->common.R.wesn[XHI] > 90.0)) {
+		GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -R:  Your +ky modifier for -Jp|P implies angles must be contained in the -90/+90 range (latitudes)\n");
+		return GMT_PROJECTION_ERROR;
+	}
 	if (GMT->current.proj.flip) {	/* Check restrictions */
 		if (GMT->common.R.wesn[YLO] < 0.0 || GMT->common.R.wesn[YHI] > GMT->current.proj.flip_radius) {
 			GMT_Report (GMT->parent, GMT_MSG_ERROR, "-JP...+f requires s >= 0 and n <= %g!\n", GMT->current.proj.flip_radius);