High memory usage in getting s2 cell covering

[shubh0508]

Hello there!!

I have a use case, where I need to convert 2D polygons to S2 cells.
For some polygons, I am observing very high memory usage(~20GB) or so.
I am fetching cells with levels between 10 to 15 for a small region(<1Km^2 or so).

After creating RegionCoverer for a polygon, I am using CellUnion function call to get the cell covering of the given polygon.
On checking the issue, I found that the length of RegionCoverer PriorityQueue containing intersecting or concerning cells keeps increasing.

High memory usage leads to the docker container getting killed in my application.
Can someone please help me with this?

Example geoJSON of one of the polygons:
"""{
"type": "Polygon",
"coordinates": [
[
[
55.491351226746794,
25.421007109833486
],
[
55.493892523236426,
25.42236515986828
],
[
55.493006607451655,
25.421891733268737
],
[
55.49234900420578,
25.421906989899732
],
[
55.491351226746794,
25.421007109833486
]
]
]
}"""

[shubh0508]

On observing the length of the Priority queue for around 100K polygons, I found that its max value for a polygon was less than 1000 for almost all the polygons, except the ones which were having memory issues.

For polygons that were having issues, the maximum length of the Priority queue went up to 1,5000,000 and higher, thus causing memory issues.

[shubh0508]

Sample Code snippet for the idea(not working):
"""
cellUnion := s2.CellUnion{}
cu, err := getCellUnionForPolygon(polygon, minCellLevel, maxCellLevel, maxNumCells)
if !err.IsNil() {
fmt.Println("err: ", err)
}
cellUnion = s2.CellUnionFromUnion(cellUnion, cu)

// divide all merged cells to minCellLevel
cellUnion.Denormalize(minCellLevel, 0)

// convert []cellID to []unit64
cellIDs := make([]uint64, 0)
for _, cellID := range cellUnion {
cellIDs = append(cellIDs, uint64(cellID))
}
fmt.Println("cell_ids", cellIDs)

func getCellUnionForPolygon(polygon [][][]float64, minCellLevel int, maxCellLevel int, maxNumCells int) (s2.CellUnion) {

if minCellLevel > maxCellLevel {
	temp := maxCellLevel
	maxCellLevel = minCellLevel
	minCellLevel = temp
}

region, err := getS2RegionForPolygon(polygon)
if !err.IsNil() {
	return nil
}
rc := &s2.RegionCoverer{MaxLevel: maxCellLevel, MinLevel: minCellLevel, MaxCells: maxNumCells}
cellUnion := rc.Covering(region)
return cellUnion

}

"""

[luchenedu]

Found same problem