Simplify conversions between km and degrees

doc/rst/source/explain_-icols.rst_

@@ -1,2 +1,2 @@
-**-i**\ *cols*\ [**+l**][**+d**\ *divisor*][**+s**\ *scale*][**+o**\ *offset*][,\ *...*][,\ **t**\ [*word*]] :ref:`(more ...) <-icols_full>`
+**-i**\ *cols*\ [**+l**][**+d**\ *divisor*][**+s**\ *scale*\|\ **d**\|\ **k**][**+o**\ *offset*][,\ *...*][,\ **t**\ [*word*]] :ref:`(more ...) <-icols_full>`
     Select input columns and transformations (0 is first column, **t** is trailing text, append *word* to read one word only).

doc/rst/source/explain_-icols_full.rst_

@@ -3,7 +3,7 @@ The **-i** option
 
 **Syntax**
 
-**-i**\ *cols*\ [**+l**][**+d**\ *divisor*][**+s**\ *scale*][**+o**\ *offset*][,\ *...*][,\ **t**\ [*word*]]
+**-i**\ *cols*\ [**+l**][**+d**\ *divisor*][**+s**\ *scale*\|\ **d**\|\ **k**][**+o**\ *offset*][,\ *...*][,\ **t**\ [*word*]]
     Select specific data columns for primary input, in arbitrary order.
 
 **Description**
@@ -16,7 +16,8 @@ one of the following modifiers to any column or column range to transform the in
 
 - **+l** to take the **log10** of the input values.
 - **+d** to divide the input values by the factor *divisor* [default is 1].
-- **+s** to multiply the input values by the factor *scale* [default is 1].
+- **+s** to multiply the input values by the factor *scale* [default is 1]. Alternatively, give **d** to convert
+  km to degrees or **k** to convert degrees to km.
 - **+o** to add the given *offset* to the input values [default is 0].
 
 To read from a given column until the end of the record, leave off *stop* when specifying the column range. Normally,

doc/rst/source/std-opts-classic.rst

@@ -44,7 +44,7 @@ Common Options (Classic Mode)
      - :ref:`Segment data by detecting gaps <-g_full>`
    * - **-h**\ [**i**\|\ **o**][*n*][**+c**][**+d**][**+m**\ *segheader*][**+r**\ *remark*][**+t**\ *title*]
      - :ref:`ASCII tables have header record[s] <-h_full>`
-   * - **-i**\ *cols*\ [**+l**][**+d**\ *divide*][**+s**\ *scale*][**+o**\ *offset*][,\ *...*][,\ **t**\ [*word*]]
+   * - **-i**\ *cols*\ [**+l**][**+d**\ *divide*][**+s**\ *scale*\|\ **d**\|\ **k**][**+o**\ *offset*][,\ *...*][,\ **t**\ [*word*]]
      - :ref:`Selection of input columns <-icols_full>`
    * - **-je**\|\ **f**\|\ **g**
      - :ref:`Mode of spherical distance calculation <-distcalc_full>`

doc/rst/source/std-opts.rst

@@ -40,7 +40,7 @@ Common Options
      - :ref:`Segment data by detecting gaps <-g_full>`
    * - **-h**\ [**i**\|\ **o**][*n*][**+c**][**+d**][**+m**\ *segheader*][**+r**\ *remark*][**+t**\ *title*]
      - :ref:`ASCII tables have header record[s] <-h_full>`
-   * - **-i**\ *cols*\ [**+l**][**+d**\ *divide*][**+s**\ *scale*][**+o**\ *offset*][,\ *...*][,\ **t**\ [*word*]]
+   * - **-i**\ *cols*\ [**+l**][**+d**\ *divide*][**+s**\ *scale*\|\ **d**\|\ **k**][**+o**\ *offset*][,\ *...*][,\ **t**\ [*word*]]
      - :ref:`Selection of input columns <-icols_full>`
    * - **-je**\|\ **f**\|\ **g**
      - :ref:`Mode of spherical distance calculation <-distcalc_full>`

src/gmt_init.c

@@ -7703,7 +7703,7 @@ void gmtlib_explain_options (struct GMT_CTRL *GMT, char *options) {
 			GMT_Usage (API, 3, "+l Take log10 of column before any other transformations.");
 			GMT_Usage (API, 3, "+d Divide column by appended <divisor>.");
 			GMT_Usage (API, 3, "+o Add to column the appended <offset>.");
-			GMT_Usage (API, 3, "+s Multiply column by appended <scale>.");
+			GMT_Usage (API, 3, "+s Multiply column by appended <scale> or give d (convert km to degree) or k (degree to km)");
 			break;
 
 		case 'A':	/* -j option for spherical distance calculation mode */
@@ -9113,10 +9113,17 @@ int gmt_parse_i_option (struct GMT_CTRL *GMT, char *arg) {
 				pos_p = 0;	/* Reset to start of new word */
 				while (gmt_getmodopt (GMT, 'i', c, "dlos", &pos_p, word, &uerr) && uerr == 0) {
 					switch (word[0]) {
+						case 'd': convert |= 1;	scale = 1.0 / atof (&word[1]); break;
 						case 'l': convert |= 2; break;
 						case 'o': convert |= 1; offset = atof (&word[1]); break;
-						case 's': convert |= 1; scale  = atof (&word[1]); break;
-						case 'd': convert |= 1; scale  = 1.0 / atof (&word[1]); break;
+						case 's':	/* Must check for special codes k (convert degrees to km) and d (convert km to degrees) */
+							convert |= 1;
+							switch (word[1]) {
+								case 'k': scale = GMT->current.proj.DIST_KM_PR_DEG; break;
+								case 'd': scale = 1.0 / GMT->current.proj.DIST_KM_PR_DEG; break;
+								default: scale  = atof (&word[1]); break;
+							}
+							break;
 						default: break;	/* These are caught in gmt_getmodopt so break is just for Coverity */
 					}
 				}

src/gmt_synopsis.h

@@ -126,7 +126,7 @@
 #define GMT_f_OPT	"-f[i|o]<colinfo>"
 #define GMT_g_OPT	"-gx|y|z|d|X|Y|D<gap>[<unit>][+a][+c<col>][+n|p]"
 #define GMT_h_OPT	"-h[i|o][<nrecs>][+c][+d][+m<segheader>][+r<remark>][+t<title>]"
-#define GMT_i_OPT	"-i<cols>[+l][+d<divisor>][+s<scale>][+o<offset>][,...][,t[<word>]]"
+#define GMT_i_OPT	"-i<cols>[+l][+d<divisor>][+s<scale>|d|k][+o<offset>][,...][,t[<word>]]"
 #define GMT_j_OPT	"-je|f|g"
 #define GMT_l_OPT	"-l[<label>][+D<pen>][+G<gap>][+H<header>][+L[<code>/]<txt>][+N<cols>][+S<size>[/<height>]][+V[<pen>]][+f<font>][+g<fill>][+j<just>][+o<dx>[/<dy>]][+p<pen>][+s<scale>][+w<width>]"
 #ifdef DEBUG