Adds support for equirectangular projection

see #30

Convert.go

@@ -27,6 +27,7 @@ const (
 	WorldMercator          = EPSG3395
 	EPSG3857               = 3857
 	WebMercator            = EPSG3857
+	EPSG4087               = 4087
 )
 
 // ensure only one person is updating our cache of converters at a time
@@ -69,6 +70,7 @@ var conversions = map[EPSGCode]*conversion{}
 var projStrings = map[EPSGCode]string{
 	EPSG3395: "+proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +datum=WGS84",                            // TODO: support +units=m +no_defs
 	EPSG3857: "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0", // TODO: support +units=m +nadgrids=@null +wktext +no_defs
+	EPSG4087: "+proj=eqc +lat_ts=0 +lat_0=0 +lon_0=0 +x_0=0 +y_0=0 +datum=WGS84",
 }
 
 // newConversion creates a conversion object for the destination systems. If

Convert_test.go

@@ -53,6 +53,17 @@ var testcases = []testcase{
 			-8641240.37, 4697899.31,
 		},
 	},
+	{
+		dest: proj.EPSG4087,
+		expectedA: []float64{
+			-14221.96, 5733772.09,
+			261848.16, 5438693.39,
+			1391089.10, 4664596.47,
+		},
+		expectedB: []float64{
+			-8641240.37, 4322963.96,
+		},
+	},
 }
 
 func TestConvert(t *testing.T) {

gie/Gie.go

@@ -25,6 +25,7 @@ var supportedProjections = []string{
 	"merc",
 	"airy",
 	"august",
+	"eqc"
 }
 
 // If the proj string has one of these keys, we won't execute the Command.

operations/Eqc.go

@@ -0,0 +1,78 @@
+package operations
+
+import (
+	"math"
+
+	"github.com/go-spatial/proj/core"
+	"github.com/go-spatial/proj/merror"
+)
+
+func init() {
+	core.RegisterConvertLPToXY("eqc",
+		"Equidistant Cylindrical (Plate Carree)",
+		"\n\tCyl, Sph\n\tlat_ts=[, lat_0=0]",
+		NewEqc,
+	)
+}
+
+// Eqc implements core.IOperation and core.ConvertLPToXY
+type Eqc struct {
+	core.Operation
+	rc float64
+}
+
+// NewEqc creates a new Plate Carree system
+func NewEqc(system *core.System, desc *core.OperationDescription) (core.IConvertLPToXY, error) {
+	op := &Eqc{}
+	op.System = system
+
+	err := op.eqcSetup(system)
+	if err != nil {
+		return nil, err
+	}
+	return op, nil
+}
+
+// Forward goes forewards
+func (op *Eqc) Forward(lp *core.CoordLP) (*core.CoordXY, error) {
+	return op.spheroidalForward(lp)
+}
+
+// Inverse goes backwards
+func (op *Eqc) Inverse(xy *core.CoordXY) (*core.CoordLP, error) {
+	return op.spheroidalReverse(xy)
+}
+
+//---------------------------------------------------------------------
+
+func (op *Eqc) spheroidalForward(lp *core.CoordLP) (*core.CoordXY, error) { /* Ellipsoidal, forward */
+	xy := &core.CoordXY{X: 0.0, Y: 0.0}
+
+	P := op.System
+
+	xy.X = op.rc * lp.Lam
+	xy.Y = lp.Phi - P.Phi0
+	return xy, nil
+}
+
+func (op *Eqc) spheroidalReverse(xy *core.CoordXY) (*core.CoordLP, error) { /* Ellipsoidal, inverse */
+	lp := &core.CoordLP{Lam: 0.0, Phi: 0.0}
+
+	P := op.System
+
+	lp.Lam = xy.X / op.rc
+	lp.Phi = xy.Y + P.Phi0
+	return lp, nil
+}
+
+func (op *Eqc) eqcSetup(sys *core.System) error {
+	ps := op.System.ProjString
+
+	latts, _ := ps.GetAsFloat("lat_ts")
+	if math.Cos(latts) <= 0 {
+		return merror.New(merror.LatTSLargerThan90)
+	}
+	op.rc = math.Cos(latts)
+
+	return nil
+}

operations/operations_test.go

@@ -101,6 +101,22 @@ var testdata = []data{
 		fwd: [][]float64{
 			{2, 1, 223404.978180972, 111722.340289763},
 		},
+	}, {
+		// builtins.gie:1104
+		proj:  "proj=eqc   +a=6400000    +lat_1=0.5 +lat_2=2",
+		delta: 0.1 * 0.001,
+		fwd: [][]float64{
+			{2, 1, 223402.144255274, 111701.072127637},
+			{2, -1, 223402.144255274, -111701.072127637},
+			{-2, 1, -223402.144255274, 111701.072127637},
+			{-2, -1, -223402.144255274, -111701.072127637},
+		},
+		inv: [][]float64{
+			{200, 100, 0.001790493, 0.000895247},
+			{200, -100, 0.001790493, -0.000895247},
+			{-200, 100, -0.001790493, 0.000895247},
+			{-200, -100, -0.001790493, -0.000895247},
+		},
 	},
 }
 
@@ -186,3 +202,16 @@ func BenchmarkConvertAiry(b *testing.B) {
 		_, _ = op.Forward(input)
 	}
 }
+
+func BenchmarkConvertEqc(b *testing.B) {
+	ps, _ := support.NewProjString("+proj=eqc +a=6400000 +lat_1=0.5 +lat_2=2")
+	_, opx, _ := core.NewSystem(ps)
+	op := opx.(core.IConvertLPToXY)
+	input := &core.CoordLP{Lam: support.DDToR(12.0), Phi: support.DDToR(55.0)}
+
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		_, _ = op.Forward(input)
+	}
+}