Collections API: Implement RasterGroupedAverage

[rajadain]

Add support for the RasterGroupedAverage operation.

Sample input: nlcd-kfactor-request.json.txt

Expected output: nlcd-kfactor-response.json.txt

Depends on #51

[mmcfarland]

Include optimizations made via #47

[rajadain]

Here's an example of RasterGroupedAverage without any rasters to group by:

awc-request.json.txt

awc-response.json.txt

[kellyi]

#65 is mostly ready for a look, I think, except that I'm getting some slightly output values for the original nlcd-kfactor-request input. Here's what the implementation in #65 currently returns:

{
	"result": {
		"List(42)": 0.22445346552610787,
		"List(22)": 0.20668663718780375,
		"List(43)": 0.23152918045304285,
		"List(71)": 0.26530274008653,
		"List(41)": 0.2639788878915292,
		"List(21)": 0.23288021817461474,
		"List(24)": 0.17446897070338138,
		"List(31)": 0.2255980250794072,
		"List(90)": 0.2502959564896539,
		"List(52)": 0.2708109404806156,
		"List(11)": 0.17810512682757315,
		"List(23)": 0.1956562087269768,
		"List(82)": 0.2680885086530039,
		"List(81)": 0.2662300594180988,
		"List(95)": 0.30244740773923695
	}
}

The values for the RasterGroupedAverage op with no rasters to group by are the same:

{
	"result": {
		"List(0)": 9.937211446569115
	}
}

[kellyi]

Wonder if the discrepancy above is related to the misalignment issue? @rajadain do you have any other sample inputs to test for the rasterGroupedAverage op with rasters supplied to test?

[rajadain]

The sample input provided above does use misaligned layers, since NLCD and KFactor belong to different generations of rasters WikiWatershed/model-my-watershed#2153. There should only be a difference if there is a tile that is not being selected. I'll try and generate a screenshot using the shape and layers in the input to see if we're missing tiles.

[rajadain]

Hmm, so while there is some misalignment, we are still selecting the correct tiles:

So the numbers should be identical.

[kellyi]

Thanks for checking that! Something's probably off in the implementation then.

[kellyi]

I'm getting some slightly output values for the original nlcd-kfactor-request input

Turns out this happens when using a list to store the values, then doing list.sum / list.length for the average. Using an (accumulator: DoubleAdder, counter: LongAdder) then doing accumulator / counter instead brings them back into alignment.