diff --git a/cngt/cngt.c b/cngt/cngt.c
index 74dfac9..0011ac6 100644
--- a/cngt/cngt.c
+++ b/cngt/cngt.c
@@ -25,7 +25,7 @@
 static double pos_x[MAX_POS];
 static double pos_y[MAX_POS];
 static double z0, height;
-static double x, y, z;
+static double cx, cy, cz;
 
 
 #define UNITS(mm)	((mm)*40.0)
@@ -33,20 +33,21 @@ static double x, y, z;
 
 static void move(void)
 {
-	serial_printf("!PZ%.1f,0;PD%.1f,%.1f\n", UNITS(z), UNITS(x), UNITS(y));
+	serial_printf("!PZ%.1f,0;PD%.1f,%.1f\n",
+	    UNITS(cz), UNITS(cx), UNITS(cy));
 }
 
 
 static void up(void)
 {
-	z = z0+height;
+	cz = z0+height;
 	move();
 }
 
 
 static void down(void)
 {
-	z = z0;
+	cz = z0;
 	move();
 }
 
@@ -62,22 +63,22 @@ static int do_key(char c)
 		break;
 	case 'h':
 		up();
-		x -= STEP;
+		cx -= STEP;
 		move();
 		break;
 	case 'j':
 		up();
-		y -= STEP;
+		cy -= STEP;
 		move();
 		break;
 	case 'k':
 		up();
-		y += STEP;
+		cy += STEP;
 		move();
 		break;
 	case 'l':
 		up();
-		x += STEP;
+		cx += STEP;
 		move();
 		break;
 	case 'q':
@@ -86,14 +87,54 @@ static int do_key(char c)
 		if (c < '0' || c > '9')
 			break;
 		up();
-		x = pos_x[c-'0'];
-		y = pos_y[c-'0'];
+		cx = pos_x[c-'0'];
+		cy = pos_y[c-'0'];
 		move();
 	}
 	return 0;
 }
 
 
+static void gp_minmax(const char *name,
+    double *xa, double *ya, double *xb, double *yb)
+{
+	FILE *file;
+	char buf[1024];
+	double x, y, z;
+	int n;
+	int first = 1;
+
+	file = fopen(name, "r");
+	if (!file) {
+		perror(name);
+		exit(1);
+	}
+	while (fgets(buf, sizeof(buf), file)) {
+		if (*buf == '#')
+			continue;
+		n = sscanf(buf, "%lf %lf %lf\n", &x, &y, &z);
+		switch (n) {
+		case 3:
+			/* fall through */
+		case 2:
+			if (first || x < *xa)
+				*xa = x;
+			if (first || x > *xb)
+				*xb = x;
+			if (first || y < *ya)
+				*ya = y;
+			if (first || y > *yb)
+				*yb = y;
+			first = 0;
+			break;
+		default:
+			break;
+		}
+	}
+	fclose(file);
+}
+
+
 static void usage(const char *name)
 {
 	fprintf(stderr, "usage: %s z0 height (file | x y ...)\n", name);
@@ -103,27 +144,39 @@ static void usage(const char *name)
 
 int main(int argc, char **argv)
 {
+	double xa = 0, ya = 0, xb = 0, yb = 0;
 	int i;
 	char c;
 
 	if (argc < 4)
 		usage(*argv);
-	if (!(argc & 1))
-		usage(*argv);
 
 	z0 = atof(argv[1]);
 	height = atof(argv[2]);
-	for (i = 3; i != argc; i += 2) {
-		pos_x[(i-3)/2] = atof(argv[i]);
-		pos_y[(i-3)/2] = atof(argv[i+1]);
+
+	if (argc & 1) {
+		for (i = 3; i != argc; i += 2) {
+			pos_x[(i-3)/2] = atof(argv[i]);
+			pos_y[(i-3)/2] = atof(argv[i+1]);
+		}
+	} else {
+		if (argc != 4)
+			usage(*argv);
+		gp_minmax(argv[3], &xa, &ya, &xb, &yb);
+		pos_x[1] = pos_x[4] = pos_x[7] = xa;
+		pos_x[2] = pos_x[5] = pos_x[8] = (xa+xb)/2;
+		pos_x[3] = pos_x[6] = pos_x[9] = xb;
+		pos_y[1] = pos_y[2] = pos_y[3] = ya;
+		pos_y[4] = pos_y[5] = pos_y[6] = (ya+yb)/2;
+		pos_y[7] = pos_y[8] = pos_y[9] = yb;
 	}
 
 	serial_open("/dev/ttyUSB0");
 	serial_printf("\nIN;!MC0\n");
 
-	x = pos_x[0];
-	y = pos_y[0];
-	z = z0+height;
+	cx = pos_x[0];
+	cy = pos_y[0];
+	cz = z0+height;
 	move();
 
 	while ((c = getkey()))