func drawGeoms(m image.Image, ctxt draw2d.GraphicContext, geoms ...*geos.Geometry) {
// get envelope and calculate scale fn
var env Envelope
if len(geoms) > 1 {
coll, err := geos.NewCollection(geos.GEOMETRYCOLLECTION, geoms...)
if err != nil {
log.Fatal(err)
}
union, err := coll.UnaryUnion()
if err != nil {
log.Fatal(err)
}
env = envelope(union)
} else {
env = envelope(geoms[0])
}
scale := func(x, y float64) (float64, float64) {
x = env.Px(x)*(WIDTH-2*PAD) + PAD
y = HEIGHT - (env.Py(y)*(HEIGHT-2*PAD) + PAD)
return x, y
}
var draw func(geoms ...*geos.Geometry)
draw = func(geoms ...*geos.Geometry) {
for i, g := range geoms {
// pick color
c := colors[i%len(colors)]
// switch type
_type, err := g.Type()
if err != nil {
log.Fatal(err)
}
switch _type {
case geos.POINT:
drawPoint(ctxt, g, c, 4.0, scale)
case geos.LINESTRING, geos.LINEARRING:
drawLine(ctxt, g, c, 4.0, scale)
case geos.POLYGON:
drawPolygon(ctxt, g, c, darken(c), 3.0, scale)
case geos.MULTIPOINT, geos.MULTILINESTRING, geos.MULTIPOLYGON, geos.GEOMETRYCOLLECTION:
n, err := g.NGeometry()
if err != nil {
log.Fatal(err)
}
var subgeoms []*geos.Geometry
for i := 0; i < n; i++ {
subgeoms = append(subgeoms, geos.Must(g.Geometry(i)))
}
draw(subgeoms...)
default:
log.Fatalf("unknown geometry type %v", _type)
}
}
}
draw(geoms...)
}
func ex9() {
wkt := []string{
"LINESTRING (2 10, 3 10, 4 9, 5 8)",
"LINESTRING (5 8, 6 6, 6 5)",
"LINESTRING (6 5, 9 6, 10 7, 11 9)",
"LINESTRING (11 9, 11 10, 10 11)",
"LINESTRING (6 5, 3 4, 2 3)",
"LINESTRING (2 3, 1.5 2.5, 1 1, 1 0)",
"LINESTRING (1 0, 0 0, 0 -1, 1 -2)",
"LINESTRING (1 -2, 2 -2, 3 -1, 3 0, 1 0)",
"LINESTRING (6 5, 6 3, 6.5 2.5)",
"LINESTRING (6.5 2.5, 7.5 2, 8.5 1.5)",
"LINESTRING (8.5 1.5, 9 0.5, 10 0.5, 11 1.5)",
}
var linestrings []*geos.Geometry
for i := range wkt {
linestrings = append(linestrings, geos.Must(geos.FromWKT(wkt[i])))
}
example("example9-unmerged-linestrings.png", linestrings...)
merged := geos.Must(geos.Must(geos.NewCollection(geos.MULTILINESTRING, linestrings...)).LineMerge())
example("example9-merged-linestrings.png", merged)
}