OK, it's misleading to call it substitution, rename to PROJECT.

src/warp.c

@@ -38,7 +38,7 @@ struct speckcache {
 #define COORD_WORLD  (-1)
 #define COORD_OBJECT (-2)
 
-typedef enum { DIFFROT, EXTRAPOLATE, SUBSTITUTE } warpstyle_t;
+typedef enum { DIFFROT, EXTRAPOLATE, PROJECT } warpstyle_t;
 
 
 struct svvec {
@@ -77,8 +77,7 @@ struct warpstuff {
     int degree;
     int coef0;	/* first fieldnumber of 3*degree terms: x',y',z', x'',y'',z'',... */
 
-    /* style == SUBSTITUTE ("-subst field0") */
-    /* Substitute some sequence of 3 attributes -> XYZ position */ 
+    /* style == PROJECT (from N dimensions to 3-D) */
     struct svvec sref;
     struct svvec sproj[3];
     struct svvec sadd;
@@ -201,7 +200,7 @@ struct cf *svvref( struct svvec *sv, int index )
     return &sv->v[index];
 }
 
-static int substvec( struct warpstuff *ws, struct svvec *sv, int arg, int argc, char **argv )
+static int projvec( struct warpstuff *ws, struct svvec *sv, int arg, int argc, char **argv )
 {
     int ix, ok, a;
     char *cp, *ep;
@@ -210,7 +209,7 @@ static int substvec( struct warpstuff *ws, struct svvec *sv, int arg, int argc,
     int coef = 0;
 
     svinit( sv );
-    ws->style = SUBSTITUTE;
+    ws->style = PROJECT;
     sv->maxc = -1;
     a = arg;
     /*
@@ -273,7 +272,7 @@ static int substvec( struct warpstuff *ws, struct svvec *sv, int arg, int argc,
     return err ? argc+1 : a;
 }
 
-static void substadd( struct warpstuff *ws )
+static void projadd( struct warpstuff *ws )
 {
     int i, k, r;
 
@@ -311,13 +310,13 @@ struct warpstuff *warp_setup( struct stuff *st, struct warpstuff *oldws, int arg
   for(i = 1; i < argc-1; i += 2) {
     char *optarg = argv[i+1];
     if(!strncmp(argv[i], "-w", 2) && argv[i][2] >= 'x' && argv[i][2] <= 'z') {
-	i = substvec( &tws, &tws.sproj[ argv[i][2] - 'x' ], i+1, argc, argv ) - 2;
+	i = projvec( &tws, &tws.sproj[ argv[i][2] - 'x' ], i+1, argc, argv ) - 2;
 
     } else if(!strcmp(argv[i], "-ref")) {
-	i = substvec( &tws, &tws.sref, i+1, argc, argv ) - 2;
+	i = projvec( &tws, &tws.sref, i+1, argc, argv ) - 2;
 
     } else if(!strcmp(argv[i], "-add")) {
-	i = substvec( &tws, &tws.sadd, i+1, argc, argv ) - 2;
+	i = projvec( &tws, &tws.sadd, i+1, argc, argv ) - 2;
 	if(tws.sadd.len != 3 || tws.sadd.v[0].c != 0 || tws.sadd.v[1].c != 1 || tws.sadd.v[2].c != 2) {
 	    msg("warp -add: expected dx,dy,dz");
 	    tws.sadd.len = 0;
@@ -387,7 +386,7 @@ struct warpstuff *warp_setup( struct stuff *st, struct warpstuff *oldws, int arg
     }
   }
   if(argc < 3) {
-    msg("Usage: %s  [-extrap coef0[,degree]] [-subst field0] [-f fin,fout][-p period0[f|s]][-z zerotime][-R rot][-T o2d][-F d2o] [-r rcore[,transition][w]]] [-fix x,y,z[w]|radius[w]]", argv[0]);
+    msg("Usage: %s  [-extrap coef0[,degree]] [-f fin,fout][-p period0[f|s]][-z zerotime][-R rot][-T o2d][-F d2o] [-r rcore[,transition][w]]] [-fix x,y,z[w]|radius[w]]", argv[0]);
     msg("-r : core rad. w/optional width of transition region (fraction of rcore)");
     msg("   : or (\"-\" separator) -r innercore-outercore");
     msg("-R(or -rigidrot) : add rigid rotation by \"rot\" degrees to entire body.");
@@ -400,8 +399,8 @@ struct warpstuff *warp_setup( struct stuff *st, struct warpstuff *oldws, int arg
     return NULL;
   }
 
-  if(tws.style == SUBSTITUTE)
-      substadd( &tws );		/* fill in sfadd[] terms: sum of sadd[] and sref dot sproj */
+  if(tws.style == PROJECT)
+      projadd( &tws );		/* fill in sfadd[] terms: sum of sadd[] and sref dot sproj */
 
   ws = oldws ? oldws : NewN( struct warpstuff, 1 );
   if(tws.tunit == 0)
@@ -530,7 +529,7 @@ void warpspecks( struct warpstuff *ws,
     }
     break;
 
-  case SUBSTITUTE: {
+  case PROJECT: {
 	int k;
 	int maxval = SPECKMAXVAL(osl);
 	int maxcoef = ws->sproj[0].maxc > ws->sproj[1].maxc ? ws->sproj[0].maxc : ws->sproj[1].maxc;