try fixing cone 'absolute' scaling

Author: etpinard

src/traces/cone/attributes.js

@@ -112,20 +112,26 @@ var attrs = {
         editType: 'calc',
         dflt: 'scaled',
         description: [
-            'Sets the mode by which the cones are sized.',
-            'If *scaled*, `sizeref` scales such that the reference cone size',
-            'for the maximum vector magnitude is 1.',
-            'If *absolute*, `sizeref` scales such that the reference cone size',
-            'for vector magnitude 1 is one grid unit.'
+            'Determines whether `sizeref` is set as a *scaled* (i.e unitless) scalar',
+            '(normalized by the max u/v/w norm in the vector field) or as',
+            '*absolute* value (in unit of velocity).'
         ].join(' ')
     },
     sizeref: {
         valType: 'number',
         role: 'info',
         editType: 'calc',
         min: 0,
-        dflt: 1,
-        description: 'Sets the cone size reference value.'
+        description: [
+            'Adjusts the cone size scaling.',
+            'The size of the cones is determined by their u/v/w norm multiplied a factor and `sizeref`.',
+            'This factor (computed internally) corresponds to the minimum "time" to travel across two',
+            'two successive x/y/z positions at the average velocity of those two successive positions',
+            'All cones in a given trace use the same factor.',
+            'With `sizemode` set to *scaled*, `sizeref` is unitless, its default value is *0.5*',
+            'With `sizemode` set to *absolute*, `sizeref` has units of velocity, its the default value is',
+            'half the sample\'s maximum vector norm.'
+        ].join(' ')
     },
 
     anchor: {

src/traces/cone/convert.js

@@ -59,7 +59,6 @@ function zip3(x, y, z) {
 }
 
 var axisName2scaleIndex = {xaxis: 0, yaxis: 1, zaxis: 2};
-var sizeMode2sizeKey = {scaled: 'coneSize', absolute: 'absoluteConeSize'};
 var anchor2coneOffset = {tip: 1, tail: 0, cm: 0.25, center: 0.5};
 var anchor2coneSpan = {tip: 1, tail: 1, cm: 0.75, center: 0.5};
 
@@ -88,15 +87,21 @@ function convert(scene, trace) {
 
     coneOpts.colormap = parseColorScale(trace.colorscale);
     coneOpts.vertexIntensityBounds = [trace.cmin / trace._normMax, trace.cmax / trace._normMax];
-
-    coneOpts[sizeMode2sizeKey[trace.sizemode]] = trace.sizeref;
     coneOpts.coneOffset = anchor2coneOffset[trace.anchor];
 
-    var meshData = conePlot(coneOpts);
+    if(trace.sizemode === 'scaled') {
+        // unitless sizeref
+        coneOpts.coneSize = trace.sizeref || 0.5;
+    } else {
+        // sizeref here has unit of velocity
+        coneOpts.coneSize = (trace.sizeref / trace._normMax) || 0.5;
+    }
 
+    var meshData = conePlot(coneOpts);
 
     // pass gl-mesh3d lighting attributes
-    meshData.lightPosition = [trace.lightposition.x, trace.lightposition.y, trace.lightposition.z];
+    var lp = trace.lightposition;
+    meshData.lightPosition = [lp.x, lp.y, lp.z];
     meshData.ambient = trace.lighting.ambient;
     meshData.diffuse = trace.lighting.diffuse;
     meshData.specular = trace.lighting.specular;
@@ -105,8 +110,7 @@ function convert(scene, trace) {
     meshData.opacity = trace.opacity;
 
     // stash autorange pad value
-    trace._pad = anchor2coneSpan[trace.anchor] * meshData.vectorScale * trace.sizeref;
-    if(trace.sizemode === 'scaled') trace._pad *= trace._normMax;
+    trace._pad = anchor2coneSpan[trace.anchor] * meshData.vectorScale * meshData.coneScale * trace._normMax;
 
     return meshData;
 }