--- a/webapp/src/main/webapp/jquery/jquery.digilib.geometry.js	Sun Mar 01 12:17:52 2015 +0100
+++ b/webapp/src/main/webapp/jquery/jquery.digilib.geometry.js	Sun Mar 01 23:26:12 2015 +0100
@@ -144,6 +144,14 @@
                 y : other.y - this.y
             });
         };
+        // returns other position scaled by ratio with regard to this point
+        that.scale = function(other, ratio) {
+            var d = this.delta(other);
+            return position({
+                x : this.x + d.x * ratio,
+                y : this.y + d.y * ratio
+            });
+        };
         // adjusts CSS position of $elem to this position
         that.adjustDiv = function($elem) {
             $elem.offset({
@@ -275,34 +283,37 @@
             this.dy = vector[1];
             return this;
             };
-        // vector
+        // return a vector with the contrary direction
         that.invertedVector = function() {
-            return [-this.dx, -this.dy];
+            return [-this.dx, -this.dy];rectifiedDist
             };
-        // perpendicular vector
+        // return a vector that is perpendicular to this line
         that.perpendicularVector = function(clockwise) {
             return clockwise ? [-this.dy, this.dx] : [this.dy, -this.dx];
             };
-        // vector distance
+        // return vector distance
         that.dist = function() {
             return Math.sqrt(this.dx * this.dx + this.dy * this.dy);
             };
+        // multiply vector with a ratio
+        that.scale = function(ratio) {
+            this.dx *= ratio;
+            this.dy *= ratio
+            return this;
+            };
         // get/set vector length
         that.length = function(length) {
             var dist = this.dist();
             if (length == null) {
                 return dist;
                 }
-            var ratio = length/dist;
-            this.dx *= ratio;
-            this.dy *= ratio
-            return this;
+            return this.scale(length/dist);
             };
-        // slope
+        // return the slope
         that.slope = function() {
             return this.dx/this.dy;
             };
-        // return a copy
+        // return a copy of this line
         that.copy = function() {
             return line(position(this.x, this.y), this.vector());
             };
@@ -311,17 +322,17 @@
             this.vector(this.invertedVector);
             return this;
             };
-        // return a parallel through a point
+        // return a parallel line through a point (with the same vector)
         that.parallel = function(p) {
             return line(position(p.x, p.y), this.vector());
             };
-        // return perpendicular line, with optional directon or other point
+        // return a perpendicular line from the origin (optionally from another point) with direction
         that.perpendicular = function(p, clockwise) {
             var point = (p == null || p.x == null)
                 ? position(this.x, this.y) : p;
             return line(point, this.perpendicularVector(clockwise));
             };
-        // return perpendicular point on line
+        // return the intersection with a perpendicular line through a point
         that.perpendicularPoint = function(p) {
             return this.intersection(this.perpendicular(p));
             };

--- a/webapp/src/main/webapp/jquery/jquery.digilib.measure.js	Sun Mar 01 12:17:52 2015 +0100
+++ b/webapp/src/main/webapp/jquery/jquery.digilib.measure.js	Sun Mar 01 23:26:12 2015 +0100
@@ -727,7 +727,7 @@
                 fill : 'none'
                 },
             guide : {
-                stroke : 'green',
+                stroke : 'blue',
                 strokewidth : 1,
                 fill : 'none'
                 },
@@ -863,6 +863,9 @@
         if (keystate['y'] != null) { // change only y-Dimension of mouse pointer
             manipulatePosition(shape, lockDimension('x'));
             }
+        if (keystate['s'] != null) { // snap to next unit
+            manipulatePosition(shape, snaptoUnit(data));
+            }
         // console.debug('onPositionShape', shape.properties.screenpos);
     };
 
@@ -900,24 +903,28 @@
         return Math.round(num * 10000 + 0.00001) / 10000
         };
 
-    // calculate the distance of the first 2 points of a shape (rectified digilib coords)
+    // calculate the distance of a shape vertex to the next (rectified digilib coords)
+    var getVertexDistance = function(data, shape, index) {
+        var vtx = shape.properties.vtx;
+        if (index == null) {
+             index = vtx == 0 ? 1 : vtx; }
+        var coords = shape.geometry.coordinates;
+        var next = (index < coords.length-1) ? index+1 : 0;
+        var dist = fn.getDistance(data, geom.position(coords[index]), geom.position(coords[next]));
+        return dist.rectified;
+        };
+
+    // calculate the measured distance for a shape (in rectified digilib coords)
     var rectifiedDist = function(data, shape) {
         var coords = shape.geometry.coordinates;
         if (shape.geometry.type === 'LineString') {
-            var pos1 = geom.position(coords[0]);
             var total = 0;
-            for (i = 1; i < coords.length; i++) {
-                var pos2 = geom.position(coords[i]);
-                var dist = fn.getDistance(data, pos1, pos2);
-                total += dist.rectified;
-                pos1 = pos2;
+            for (v = 0; v < coords.length-1; v++) {
+                total += getVertexDistance(data, shape, v);
                 }
             return total;
         } else {
-            var v = shape.properties.vtx;
-            if (v === 0) {v = 1}
-            var dist = fn.getDistance(data, geom.position(coords[v]), geom.position(coords[v-1]));
-            return dist.rectified;
+            return getVertexDistance(data, shape);
             }
         };
 
@@ -1040,6 +1047,24 @@
         };
 
     // returns a screenpoint manipulation function
+    var snaptoUnit = function(data) {
+        // lock one dimension of the current screen pos to that of the previous
+        var snap = function(shape) {
+            var props = shape.properties;
+            var startpos = props.startpos;
+            var screenpos = props.screenpos;
+            var vtx = props.vtx;
+            if (startpos == null || screenpos == null || vtx == null) {
+                return; }
+            var fac = data.measureFactor;
+            var dist = getVertexDistance(data, shape) * fac;
+            var round = Math.round(dist);
+            screenpos[vtx] = startpos.scale(screenpos[vtx], round/dist);
+            }
+        return snap;
+        };
+
+    // returns a screenpoint manipulation function
     var lockDimension = function(dim) {
         // lock one dimension of the current screen pos to that of the previous
         var lock = function(shape) {
@@ -1197,15 +1222,17 @@
             removeSelectedShapes(data);
             return false;
             }
-        // keys 'x' and 'y': immediate response, lock dimension and redraw shape
+        // immediate key response, fire drag event
         if (code === 88 || key === 'x' ||
-            code === 89 || key === 'y') {
+            code === 89 || key === 'y' ||
+            code === 83 || key === 's') {
             if (currentShape == null) { return true };
             var props = currentShape.properties;
             var pt = props.screenpos[props.vtx]; // get last recorded mouse position
             var eventpos = { pageX: pt.x, pageY: pt.y }
             var evt = jQuery.Event("mousemove.dlVertexDrag", eventpos);
             $(document).trigger(evt);
+            return false;
             }
         // console.debug('measure: keyDown', code, event.key, keystate);
         };
@@ -1216,6 +1243,7 @@
         var key = event.key;
         delete keystate[key]; // invalidate key state
         // console.debug('measure: keyUp', code, event.key, keystate);
+        return false;
         };
 
     // attach/detach keyup/down event handlers
@@ -1461,6 +1489,9 @@
         widgets.value1.on('change.measure', function(evt) { changeFactor(data) });
         widgets.unit1.on('change.measure',  function(evt) { convertUnits(data) });
         widgets.unit2.on('change.measure',  function(evt) { convertUnits(data) });
+        widgets.unit1.attr('tabindex', -1);
+        widgets.unit2.attr('tabindex', -1);
+        widgets.value1.attr('tabindex', -1);
         };
 
     // event handler for setup phase