FIX: check whether -C and -E use different unit in grdtrack (#8728)

* FIX: check whether -C and -E use different unit

* DOC: update annotation of checking -C and -E units

* DOC: update grdtrack.rst about -C and -E units

* DOC: update grdtrack.rst, add PR reference

Author: Dengda98

doc/rst/source/grdtrack.rst

@@ -139,6 +139,9 @@ Optional Arguments
     counter-clockwise.  Finally, you can use **+f** to set a fixed azimuth
     for all profiles. **Note**: If |-C| is set and *spacing* is given then
     that sampling scheme overrules any modifier set in |-E|.
+    Currently, there is a bug when |-C| and |-E| use different units 
+    (see PR `#8728 <https://github.com/GenericMappingTools/gmt/pull/8728>`_ ).
+    If you use both, please manually specify the same unit for each.
 
 .. _-D:
 

src/grdtrack.c

@@ -815,6 +815,16 @@ EXTERN_MSC int GMT_grdtrack (void *V_API, int mode, void *args) {
 		}
 		if (gmt_init_distaz (GMT, Ctrl->E.unit, Ctrl->E.mode, GMT_MAP_DIST) == GMT_NOT_A_VALID_TYPE)	/* Initialize the distance unit and scaling */
 			Return (GMT_NOT_A_VALID_TYPE);
+			
+		/* !!! TEMPORARY METHOD !!! */
+		/* Currently we cannot use different units in -C and -E, we have to prevent this bug first. See PR #8728 */
+		/* Check whether -C and -E use different unit */
+		if (Ctrl->C.active && Ctrl->C.unit != Ctrl->E.unit){
+			GMT_Report (API, GMT_MSG_ERROR, 
+				"Option -C and -E shoule take the same unit, but received %c (-C) and %c (-E). "
+				"Recommend you explicitly set the same unit for -C and -E.\n", Ctrl->C.unit, Ctrl->E.unit);
+			Return (GMT_RUNTIME_ERROR);
+		}
 
 		/* Set default spacing to half the min grid spacing: */
 		Ctrl->E.step = 0.5 * MIN (GC[0].G->header->inc[GMT_X], GC[0].G->header->inc[GMT_Y]);