Address feedback

dev-docs/RFCs/v7.x/gpu-grid-layer.md

@@ -2,7 +2,7 @@
 
 * **Authors**: Ravi Akkenapally
 * **Date**: May 2019
-* **Status**: **Draft**
+* **Status**: **Review**
 
 
 ## Abstract
@@ -27,14 +27,53 @@ There are several features of `GridLayer` that can't be supported by GPU Aggrega
 
 ## Color and Elevation Accessors
 
-`GridLayer`'s `getColor` and `getElevation` perform two things. 1. Specify which field in original data set to use as weight and 2. aggregation operation. To support GPU Aggregation, these accessor props need to be split into two new props.
+`GridLayer`'s `getColor` and `getElevation` perform two things. 1. Specify which field in original data set to use as weight and 2. aggregation operation. To support GPU Aggregation weight and operation have to be split, and introduce two new props `colorAggregation` and `elevationAggregation`. Each of these props is an object with following fields :
 
-    1.`getColorWeight/getElevationWeight`: specifies weight field of each data point.
-    2.`colorAggregation/elevationAggregation`:  SUM, MIN, MAX or MEAN
+    * `operation` (`Enum`): Defines type of aggregation , which could be SUM, MIN, MAX or MEAN.
+    * `weight` (`Number`, `String` or `Function`): Defines weight of each individual point. When `Number` is specified, that value is used as weight, when `String` is specified, it is used as a key to access weight from data object and when `Funciton` is specified, it is called by passing data object and should return a weight.
 
-So in addition to `getColor` and `getElevation` props, we will add `getColorWeight`, `getElevationWeight`, `colorAggregation` and `elevationAggregation`. For any custom aggregations, we will exclusively specify existing props, `getColor/ElevationValue` and fallback to CPU Aggregation. If GPU Aggregation is required users must specify new props.
+    For example: `colorAggregation: {operation: SUM, weight: 'SPACES'};`
+
+So in addition to `getColor` and `getElevation` props, we will add `colorAggregation`, and `weightAggregation` props. For any custom aggregations, we will exclusively specify existing props, `getColor/ElevationValue` and fallback to CPU Aggregation. If GPU Aggregation is required users must specify new props.
+
+
+## Picking
+
+When aggregation is performed on CPU, each cell can point to an array of objects that fall into the cell. And when a cell is picked, `GridLayer` can provide this array of objects. But when using GPU Aggregation, picking information will be limited to `aggregated value` of the cell and `domain value` (min/max value of all aggregated cells). To provide same information as existing `GridLayer` while using GPU Aggregation, we will perform CPU Aggregation and provide the list. This will introduce a delay but should only happen when user requests picking information programatically. For picking during mouse over, we will provide current cell values by reading GPU aggregation results.
 
 
 ## Changes to GridLayer
 
 Existing `GridLayer` will be renamed to `CPUGridLayer` and a new composite layer replaces `GridLayer`. This new composite layer, based on props and user settings, will either construct `CPUGridLayer` or `GPUGridLayer`.
+
+
+## Some Aggregation API Ideas that need more investigation
+
+
+### Lower/Higher Percentile
+
+Intention of this prop is to remove a few "outliers" in the input data that skew things too much. Currently this is done on aggregated values. But we can do the same on non aggregated data, by filtering this on GPU, in that way, we don't need to perform sorting and hence don't need to fallback to CPU.
+
+### Common Aggregation API
+
+Deck.gl has 4 aggregation layers, and 3 layers support GPU Aggregation (including `GridLayer`), and new aggregation layer might be added in future. Following is an idea support consistent API to specify aggregation props.
+
+Aggregation can be defined outside of the layer
+
+```
+  const aggregator = new Aggregator({
+    aggregations: {
+      COUNT_SUM: {aggregation: 'SUM', field: 'count'},
+      VALUE_MEAN: {aggregation: 'MEAN', field: 'value'}
+    }
+  });
+```    
+
+and its result can be feed into the one ore more layers.
+
+```
+   color: aggregator.COUNT_SUM,
+   colorScale: ..., // Some format that can be GLSL compiled
+   elevation: aggregator.VALUE_MIN,
+   ...
+```