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Using Multipolygons for more efficient joins #104

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geoHeil opened this issue Jun 11, 2017 · 1 comment

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@geoHeil
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commented Jun 11, 2017

I have polygons which look like https://i.stack.imgur.com/w6yup.png and there are lots of them which lead to a gigantic consumption of RAM #91 as well as a very cpu intensive task for https://github.com/DataSystemsLab/GeoSpark/blob/master/core/src/main/java/org/datasyslab/geospark/spatialOperator/JoinQuery.java#L87

Description of my case: as you see in the link an object will emit 2-3k polygons and I have roughly speaking 100000 objects. For each polygon there is an ID which links back to the object and a value. When aggregating the polygons to multi-polygons (one per object per value) their number and thus the number of lookups should shrink considerably. Is there a possibility to implement this in geospark?

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commented Jun 11, 2017

Also http://postgis.net/2014/03/14/tip_intersection_faster/

Doing an ST_Intersection is much slower than relation checks such as ST_Intersects , ST_CoveredBy, and , ST_Within . In many situations you know the intersection of 2 geometries without actually computing an intersection. In these cases, you can skip the costly ST_Intersection call

couldnt https://github.com/DataSystemsLab/GeoSpark/blob/master/core/src/main/java/org/datasyslab/geospark/joinJudgement/GeometryByPolygonJudgementUsingIndex.java#L50-L90 be optimized to take advantage of this? (https://github.com/DataSystemsLab/GeoSpark/blob/master/core/src/main/java/org/datasyslab/geospark/joinJudgement/GeometryByPolygonJudgementUsingIndex.java#L75-L81)

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