github.com/cockroachdb/cockroach@v20.2.0-alpha.1+incompatible/pkg/geo/geomfn/linear_reference.go (about)

     1  // Copyright 2020 The Cockroach Authors.
     2  //
     3  // Use of this software is governed by the Business Source License
     4  // included in the file licenses/BSL.txt.
     5  //
     6  // As of the Change Date specified in that file, in accordance with
     7  // the Business Source License, use of this software will be governed
     8  // by the Apache License, Version 2.0, included in the file
     9  // licenses/APL.txt.
    10  
    11  package geomfn
    12  
    13  import (
    14  	"github.com/cockroachdb/cockroach/pkg/geo"
    15  	"github.com/cockroachdb/cockroach/pkg/geo/geos"
    16  	"github.com/cockroachdb/errors"
    17  	"github.com/twpayne/go-geom"
    18  	"github.com/twpayne/go-geom/encoding/ewkb"
    19  )
    20  
    21  // LineInterpolatePoints returns one or more points along the given
    22  // LineString which are at an integral multiples of given fraction of
    23  // LineString's total length. When repeat is set to false, it returns
    24  // the first point.
    25  func LineInterpolatePoints(g *geo.Geometry, fraction float64, repeat bool) (*geo.Geometry, error) {
    26  	if fraction < 0 || fraction > 1 {
    27  		return nil, errors.Newf("fraction %f should be within [0 1] range", fraction)
    28  	}
    29  	geomRepr, err := g.AsGeomT()
    30  	if err != nil {
    31  		return nil, err
    32  	}
    33  	// Empty geometries do not react well in GEOS, so we have to
    34  	// convert and check beforehand.
    35  	// Remove after #49209 is resolved.
    36  	if geomRepr.Empty() {
    37  		return geo.NewGeometryFromGeom(geom.NewPointEmpty(geom.XY))
    38  	}
    39  	switch geomRepr := geomRepr.(type) {
    40  	case *geom.LineString:
    41  		// In case fraction is greater than 0.5 or equal to 0 or repeat is false,
    42  		// then we will have only one interpolated point.
    43  		lengthOfLineString := geomRepr.Length()
    44  		if repeat && fraction <= 0.5 && fraction != 0 {
    45  			numberOfInterpolatedPoints := int(1 / fraction)
    46  			interpolatedPoints := geom.NewMultiPoint(geom.XY).SetSRID(geomRepr.SRID())
    47  			for pointInserted := 1; pointInserted <= numberOfInterpolatedPoints; pointInserted++ {
    48  				pointEWKB, err := geos.InterpolateLine(g.EWKB(), float64(pointInserted)*fraction*lengthOfLineString)
    49  				if err != nil {
    50  					return nil, err
    51  				}
    52  				point, err := ewkb.Unmarshal(pointEWKB)
    53  				if err != nil {
    54  					return nil, err
    55  				}
    56  				err = interpolatedPoints.Push(point.(*geom.Point))
    57  				if err != nil {
    58  					return nil, err
    59  				}
    60  			}
    61  			return geo.NewGeometryFromGeom(interpolatedPoints)
    62  		}
    63  		interpolatedPointEWKB, err := geos.InterpolateLine(g.EWKB(), fraction*lengthOfLineString)
    64  		if err != nil {
    65  			return nil, err
    66  		}
    67  		return geo.ParseGeometryFromEWKB(interpolatedPointEWKB)
    68  	default:
    69  		return nil, errors.Newf("geometry %s should be LineString", g.Shape())
    70  	}
    71  }