first commit

README.md

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+The [Go](http://golang.org/) package _proj_ provides an interface to the Cartographic Projections Library [PROJ](https://proj.org/).
+
+Keywords: cartography, cartographic projection
+
+*Work in progress*

v5/proj.c

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+#include "proj_go.h"
+
+int pjnull(PJ *pj) {
+    return pj == 0 ? 1 : 0;
+}
+
+void trans(PJ *pj, PJ_DIRECTION direction, double u1, double v1, double w1, double t1, double *u2, double *v2, double *w2, double *t2) {
+    PJ_COORD
+	co1,
+	co2;
+    co1.uvwt.u = u1;
+    co1.uvwt.v = v1;
+    co1.uvwt.w = w1;
+    co1.uvwt.t = t1;
+    co2 = proj_trans(pj, direction, co1);
+    *u2 = co2.uvwt.u;
+    *v2 = co2.uvwt.v;
+    *w2 = co2.uvwt.w;
+    *t2 = co2.uvwt.t;    
+}

v5/proj_go.h

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+#include <proj.h>
+#include <stdlib.h>
+
+int pjnull(PJ *pj);
+void trans(PJ *pj, PJ_DIRECTION direction, double u1, double v1, double w1, double t1, double *u2, double *v2, double *w2, double *t2);

v5/v5.go

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+package proj
+
+/*
+#cgo darwin pkg-config: proj
+#cgo !darwin LDFLAGS: -lproj
+#include "proj_go.h"
+*/
+import "C"
+
+import (
+	"errors"
+	"runtime"
+	"unsafe"
+)
+
+type Context struct {
+	pj_context *C.PJ_CONTEXT
+	opened     bool
+}
+
+type Proj struct {
+	pj      *C.PJ
+	context *Context
+	opened  bool
+}
+
+type Coord struct {
+	U, V, W, T float64
+}
+
+var (
+	errContextClosed    = errors.New("Context is closed")
+	errProjectionClosed = errors.New("Projection is closed")
+)
+
+func NewContext() *Context {
+	ctx := Context{
+		pj_context: C.proj_context_create(),
+		opened:     true,
+	}
+	runtime.SetFinalizer(&ctx, (*Context).Close)
+	return &ctx
+}
+
+func (ctx *Context) Close() {
+	if ctx.opened {
+		C.proj_context_destroy(ctx.pj_context)
+		ctx.pj_context = nil
+		ctx.opened = false
+		// TODO: destroy projections
+	}
+}
+
+func (ctx *Context) Create(definition string) (*Proj, error) {
+	if !ctx.opened {
+		return nil, errContextClosed
+	}
+
+	cs := C.CString(definition)
+	defer C.free(unsafe.Pointer(cs))
+	pj := C.proj_create(ctx.pj_context, cs)
+	if C.pjnull(pj) != 0 {
+		errno := C.proj_context_errno(ctx.pj_context)
+		err := C.GoString(C.proj_errno_string(errno))
+		return nil, errors.New(err)
+	}
+
+	p := Proj{
+		opened:  true,
+		context: ctx,
+		pj:      pj,
+	}
+
+	// TODO: projection toevoegen aan context
+
+	runtime.SetFinalizer(&p, (*Proj).Close)
+	return &p, nil
+}
+
+func (p *Proj) Close() {
+	if p.opened {
+		C.proj_destroy(p.pj)
+		p.context = nil
+		p.opened = false
+		// todo: projection verwijderen uit context
+	}
+}
+
+func (p *Proj) Fwd(coord Coord) (Coord, error) {
+	return p.trans(coord, false)
+}
+
+func (p *Proj) Inv(coord Coord) (Coord, error) {
+	return p.trans(coord, true)
+}
+
+func (p *Proj) trans(coord Coord, inverse bool) (Coord, error) {
+	if !p.opened {
+		return Coord{}, errProjectionClosed
+	}
+
+	var direction C.PJ_DIRECTION
+	if inverse {
+		direction = C.PJ_INV
+	} else {
+		direction = C.PJ_FWD
+	}
+
+	var u, v, w, t C.double
+	C.trans(p.pj, direction, C.double(coord.U), C.double(coord.V), C.double(coord.W), C.double(coord.T), &u, &v, &w, &t)
+
+	coord2 := Coord{
+		U: float64(u),
+		V: float64(v),
+		W: float64(w),
+		T: float64(t),
+	}
+	return coord2, nil
+}