diff --git a/src/kiri/worker.js b/src/kiri/worker.js
index 9c101db3..86c9945b 100644
--- a/src/kiri/worker.js
+++ b/src/kiri/worker.js
@@ -279,6 +279,7 @@ KIRI.worker = {
                 1;                         // base
             // convert png to grayscale
             let gray = new Uint8Array(width * height);
+            let alpha = new Uint8Array(width * height);
             let gi = 0;
             let invi = info.inv_image ? true : false;
             let inva = info.inv_alpha ? true : false;
@@ -291,15 +292,15 @@ KIRI.worker = {
                     let b = data[di+2];
                     let a = data[di+3];
                     let v = ((r + g + b) / 3);
+                    if (inva) a = 255 - a;
+                    if (invi) v = 255 - v;
                     if (border) {
                         if (x < border || y < border || x > width-border-1 || y > height-border-1) {
                             v = 255;
                         }
                     }
-                    if (invi) v = 255 - v;
-                    if (inva) a = 255 - a;
-                    v *= (a/255);
-                    gray[gi++] = v;
+                    alpha[gi] = a;
+                    gray[gi++] = v * (a / 255);
                 }
             }
             let blur = parseInt(info.blur || 0);
@@ -311,7 +312,8 @@ KIRI.worker = {
                         let xr = Math.min(x+1,width-1);
                         let yu = Math.max(y-1,0);
                         let yd = Math.min(y+1,height-1);
-                        blur[x + width * y] = (
+                        let id = x + width * y;
+                        blur[id] = ((
                             gray[xl + (width * yu)] +
                             gray[x  + (width * yu)] +
                             gray[xr + (width * yu)] +
@@ -321,7 +323,7 @@ KIRI.worker = {
                             gray[xl + (width * yd)] +
                             gray[x  + (width * yd)] +
                             gray[xr + (width * yd)]
-                        ) / 9;
+                        ) / 9);
                     }
                 }
                 gray = blur;
@@ -339,11 +341,12 @@ KIRI.worker = {
             // create surface vertices & faces
             for (let x = 0; x < width; x++) {
                 for (let y = 0; y < height; y++) {
-                    let v = gray[x + width * y];
+                    let id = x + width * y;
+                    let v = gray[id];
                     // create vertex @ x,y
                     verts[vi++] = (-w2 + x) / div;
                     verts[vi++] = (h2 - y) / div;
-                    verts[vi++] = ((255 - v) / 50) + base;
+                    verts[vi++] = (v / 50) + (base * alpha[id] / 255);
                     VI++;
                     // create two surface faces on the rect between x-1,y-1 and x,y
                     if (x > 0 && y > 0) {
diff --git a/src/mode/cam/prepare.js b/src/mode/cam/prepare.js
index 0c80959e..3a33e5fc 100644
--- a/src/mode/cam/prepare.js
+++ b/src/mode/cam/prepare.js
@@ -99,12 +99,12 @@
             tip2tipEmit = print.tip2tipEmit,
             poly2polyEmit = print.poly2polyEmit,
             maxToolDiam = widget.maxToolDiam,
-            terrain = widget.terrain.map(data => {
+            terrain = widget.terrain ? widget.terrain.map(data => {
                 return {
                     z: data.z,
                     tops: data.tops,
                 };
-            });
+            }) : zmax;
 
         function newLayer() {
             if (layerOut.length < 2) {
@@ -637,6 +637,9 @@
      * return tool Z clearance height for a line segment movement path
      */
     function getZClearPath(terrain, x1, y1, x2, y2, z, zadd, off, over) {
+        if (terrain > 0) {
+            return terrain + zadd + over;
+        }
         let maxz = z;
         let check = [];
         for (let i=0; i<terrain.length; i++) {
diff --git a/src/mode/cam/slice.js b/src/mode/cam/slice.js
index 6051e958..190bc7df 100644
--- a/src/mode/cam/slice.js
+++ b/src/mode/cam/slice.js
@@ -168,11 +168,12 @@
         let tslices = [];
         let tshadow = [];
         let tzindex = slicer.interval(minStepDown, { fit: true, off: 0.01, down: true, flats: true });
-        let fakeTerrain = false;
-        // if (tzindex.length > 200) {
-        //     fakeTerrain = tzindex[0];
-        //     tzindex = [ tzindex.pop() ];
-        // }
+        let skipTerrain = !(procRough || procOutline) && tzindex.length > 50;
+
+        if (skipTerrain) {
+            console.log("skipping terrain generation for speed");
+            tzindex = [ tzindex.pop() ];
+        }
 
         let terrain = slicer.slice(tzindex, { each: (data, index, total) => {
             tshadow = POLY.union(tshadow.slice().appendAll(data.tops), 0.01, true);
@@ -186,11 +187,6 @@
             }
             updateOp(index, total);
         }, genso: true });
-        if (fakeTerrain) {
-            // to avoid compute for highly detailed maps, force all
-            // moves above part top by synthesizing a single terrain slice
-            terrain[0].z = fakeTerrain.z;
-        }
 
         let shadowTop = terrain[terrain.length - 1];
         let center = tshadow[0].bounds.center();
@@ -572,7 +568,7 @@
         // dslice.output().setLayer("shadowOff", { line: 0xff0000 }).addPolys(shadowOff);
         // sliceAll.push(dslice);
 
-        widget.terrain = terrain;
+        widget.terrain = skipTerrain ? null : terrain;
         widget.minToolDiam = minToolDiam;
         widget.maxToolDiam = maxToolDiam;