David Smiley created SOLR-7005:
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Summary: facet.heatmap for spatial heatmap faceting on RPT
Key: SOLR-7005
URL: https://issues.apache.org/jira/browse/SOLR-7005
Project: Solr
Issue Type: New Feature
Components: spatial
Reporter: David Smiley
Assignee: David Smiley
Fix For: 5.1
This is a new feature that uses the new spatial Heatmap / 2D PrefixTree cell
counter in Lucene spatial LUCENE-6191. This is a form of faceting, and as-such
I think it should live in the "facet" parameter namespace. Here's what the
parameters are:
* facet=true
* facet.heatmap=fieldname
* facet.heatmap.bbox=\["-180 -90" TO "180 90"]
* facet.heatmap.gridLevel=6
* facet.heatmap.distErrPct=0.10
Like other faceting features, the fieldName can have local-params to exclude
filter queries or specify an output key.
The bbox is optional; you get the whole world or you can specify a box or
actually any shape that WKT supports (you get the bounding box of whatever you
put).
Ultimately, this feature needs to know the grid level, which together with the
input shape will yield a certain number of cells. You can specify gridLevel
exactly, or don't and instead provide distErrPct which is computed like it is
for the RPT field type as seen in the schema. 0.10 yielded ~4k cells but it'll
vary. There's also a facet.heatmap.maxCells safety net defaulting to 100k.
Exceed this and you get an error.
The output is (JSON):
{noformat}
{gridLevel=6,columns=64,rows=64,minX=-180.0,maxX=180.0,minY=-90.0,maxY=90.0,counts=[[0,
0, 2, 1, ....],[1, 1, 3, 2, ...],...]}
{noformat}
counts is null if all would be 0. Perhaps individual row arrays should
likewise be null... I welcome feedback.
I'm toying with an output format option in which you can specify a base-64'ed
grayscale PNG.
Obviously this should support sharded / distributed environments.
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