mapnik/src/proj_transform.cpp

/*****************************************************************************
 *
 * This file is part of Mapnik (c++ mapping toolkit)
 *
 * Copyright (C) 2014 Artem Pavlenko
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 *****************************************************************************/

// mapnik
#include <mapnik/global.hpp>
#include <mapnik/box2d.hpp>
#include <mapnik/projection.hpp>
#include <mapnik/proj_transform.hpp>
#include <mapnik/coord.hpp>

#ifdef MAPNIK_USE_PROJ4
// proj4
#include <proj_api.h>
#endif

// stl
#include <vector>
#include <stdexcept>

namespace mapnik {

proj_transform::proj_transform(projection const& source,
                               projection const& dest)
    : source_(source),
      dest_(dest),
      is_source_longlat_(false),
      is_dest_longlat_(false),
      is_source_equal_dest_(false),
      wgs84_to_merc_(false),
      merc_to_wgs84_(false)
{
    is_source_equal_dest_ = (source_ == dest_);
    if (!is_source_equal_dest_)
    {
        is_source_longlat_ = source_.is_geographic();
        is_dest_longlat_ = dest_.is_geographic();
        boost::optional<well_known_srs_e> src_k = source.well_known();
        boost::optional<well_known_srs_e> dest_k = dest.well_known();
        bool known_trans = false;
        if (src_k && dest_k)
        {
            if (*src_k == WGS_84 && *dest_k == G_MERC)
            {
                wgs84_to_merc_ = true;
                known_trans = true;
            }
            else if (*src_k == G_MERC && *dest_k == WGS_84)
            {
                merc_to_wgs84_ = true;
                known_trans = true;
            }
        }
        if (!known_trans)
        {
#ifdef MAPNIK_USE_PROJ4
            source_.init_proj4();
            dest_.init_proj4();
#else
            throw std::runtime_error(std::string("Cannot initialize proj_transform for given projections without proj4 support (-DMAPNIK_USE_PROJ4): '") + source_.params() + "'->'" + dest_.params() + "'");
#endif
        }
    }
}

bool proj_transform::equal() const
{
    return is_source_equal_dest_;
}

bool proj_transform::is_known() const
{
    return merc_to_wgs84_ || wgs84_to_merc_;
}

bool proj_transform::forward (double & x, double & y , double & z) const
{
    return forward(&x, &y, &z, 1);
}

bool proj_transform::forward (geometry::point<double> & p) const
{
    double z = 0;
    return forward(&(p.x), &(p.y), &z, 1);
}

unsigned int proj_transform::forward (geometry::line_string<double> & ls) const
{
    std::size_t size = ls.size();
    if (size == 0) return 0;

    if (is_source_equal_dest_)
        return 0;

    if (wgs84_to_merc_)
    {
        lonlat2merc(ls);
        return 0;
    }
    else if (merc_to_wgs84_)
    {
        merc2lonlat(ls);
        return 0;
    }

    geometry::point<double> * ptr = ls.data();
    double * x = reinterpret_cast<double*>(ptr);
    double * y = x + 1;
    double * z = NULL;
    if(!forward(x, y, z, size, 2))
    {
        return size;
    }
    return 0;
}

bool proj_transform::forward (double * x, double * y , double * z, int point_count, int offset) const
{

    if (is_source_equal_dest_)
        return true;

    if (wgs84_to_merc_)
    {
        return lonlat2merc(x,y,point_count);
    }
    else if (merc_to_wgs84_)
    {
        return merc2lonlat(x,y,point_count);
    }

#ifdef MAPNIK_USE_PROJ4
    if (is_source_longlat_)
    {
        int i;
        for(i=0; i<point_count; i++) {
            x[i*offset] *= DEG_TO_RAD;
            y[i*offset] *= DEG_TO_RAD;
        }
    }

    if (pj_transform( source_.proj_, dest_.proj_, point_count,
                      offset, x,y,z) != 0)
    {
        return false;
    }

    if (is_dest_longlat_)
    {
        int i;
        for(i=0; i<point_count; i++) {
            x[i*offset] *= RAD_TO_DEG;
            y[i*offset] *= RAD_TO_DEG;
        }
    }
#endif
    return true;
}

bool proj_transform::backward (double * x, double * y , double * z, int point_count, int offset) const
{
    if (is_source_equal_dest_)
        return true;

    if (wgs84_to_merc_)
    {
        return merc2lonlat(x,y,point_count);
    }
    else if (merc_to_wgs84_)
    {
        return lonlat2merc(x,y,point_count);
    }

#ifdef MAPNIK_USE_PROJ4
    if (is_dest_longlat_)
    {
        int i;
        for(i=0; i<point_count; i++) {
            x[i*offset] *= DEG_TO_RAD;
            y[i*offset] *= DEG_TO_RAD;
        }
    }

    if (pj_transform( dest_.proj_, source_.proj_, point_count,
                      offset, x,y,z) != 0)
    {
        return false;
    }

    if (is_source_longlat_)
    {
        int i;
        for(i=0; i<point_count; i++) {
            x[i*offset] *= RAD_TO_DEG;
            y[i*offset] *= RAD_TO_DEG;
        }
    }
#endif
    return true;
}

bool proj_transform::backward (double & x, double & y , double & z) const
{
    return backward(&x, &y, &z, 1);
}

bool proj_transform::backward (geometry::point<double> & p) const
{
    double z = 0;
    return backward(&(p.x), &(p.y), &z, 1);
}

unsigned int proj_transform::backward (geometry::line_string<double> & ls) const
{
    std::size_t size = ls.size();
    if (size == 0) return 0;

    if (is_source_equal_dest_)
        return 0;

    if (wgs84_to_merc_)
    {
        merc2lonlat(ls);
        return 0;
    }
    else if (merc_to_wgs84_)
    {
        lonlat2merc(ls);
        return 0;
    }

    geometry::point<double> * ptr = ls.data();
    double * x = reinterpret_cast<double*>(ptr);
    double * y = x + 1;
    double * z = NULL;
    if(!backward(x, y, z, size, 2))
    {
        return size;
    }
    return 0;
}

bool proj_transform::forward (box2d<double> & box) const
{
    if (is_source_equal_dest_)
        return true;

    double llx = box.minx();
    double ulx = box.minx();
    double lly = box.miny();
    double lry = box.miny();
    double lrx = box.maxx();
    double urx = box.maxx();
    double uly = box.maxy();
    double ury = box.maxy();
    double z = 0.0;
    if (!forward(llx,lly,z))
        return false;
    if (!forward(lrx,lry,z))
        return false;
    if (!forward(ulx,uly,z))
        return false;
    if (!forward(urx,ury,z))
        return false;

    double minx = std::min(ulx, llx);
    double miny = std::min(lly, lry);
    double maxx = std::max(urx, lrx);
    double maxy = std::max(ury, uly);
    box.init(minx,
             miny,
             maxx,
             maxy);
    return true;
}

bool proj_transform::backward (box2d<double> & box) const
{
    if (is_source_equal_dest_)
        return true;

    double llx = box.minx();
    double ulx = box.minx();
    double lly = box.miny();
    double lry = box.miny();
    double lrx = box.maxx();
    double urx = box.maxx();
    double uly = box.maxy();
    double ury = box.maxy();
    double z = 0.0;
    if (!backward(llx,lly,z))
        return false;
    if (!backward(lrx,lry,z))
        return false;
    if (!backward(ulx,uly,z))
        return false;
    if (!backward(urx,ury,z))
        return false;
    double minx = std::min(ulx, llx);
    double miny = std::min(lly, lry);
    double maxx = std::max(urx, lrx);
    double maxy = std::max(ury, uly);
    box.init(minx,
             miny,
             maxx,
             maxy);
    return true;
}

// Returns points in clockwise order. This allows us to do anti-meridian checks.
void envelope_points(std::vector< coord<double,2> > & coords, box2d<double>& env, int points)
{
    double width = env.width();
    double height = env.height();

    int steps;

    if (points <= 4) {
        steps = 0;
    } else {
        steps = static_cast<int>(std::ceil((points - 4) / 4.0));
    }

    steps += 1;
    double xstep = width / steps;
    double ystep = height / steps;

    coords.resize(points);
    for (int i=0; i<steps; i++) {
        // top: left>right
        coords[i] = coord<double, 2>(env.minx() + i * xstep, env.maxy());
        // right: top>bottom
        coords[i + steps] = coord<double, 2>(env.maxx(), env.maxy() - i * ystep);
        // bottom: right>left
        coords[i + steps * 2] = coord<double, 2>(env.maxx() - i * xstep, env.miny());
        // left: bottom>top
        coords[i + steps * 3] = coord<double, 2>(env.minx(), env.miny() + i * ystep);
    }
}

// determine if an ordered sequence of coordinates is in clockwise order
bool is_clockwise(const std::vector< coord<double,2> > & coords)
{
    int n = coords.size();
    coord<double,2> c1, c2;
    double a = 0.0;

    for (int i=0; i<n; i++) {
        c1 = coords[i];
        c2 = coords[(i + 1) % n];
        a += (c1.x * c2.y - c2.x * c1.y);
    }
    return a <= 0.0;
}

box2d<double> calculate_bbox(std::vector<coord<double,2> > & points) {
    std::vector<coord<double,2> >::iterator it = points.begin();
    std::vector<coord<double,2> >::iterator it_end = points.end();

    box2d<double> env(*it, *(++it));
    for (; it!=it_end; ++it) {
        env.expand_to_include(*it);
    }
    return env;
}


// More robust, but expensive, bbox transform
// in the face of proj4 out of bounds conditions.
// Can result in 20 -> 10 r/s performance hit.
// Alternative is to provide proper clipping box
// in the target srs by setting map 'maximum-extent'

bool proj_transform::backward(box2d<double>& env, int points) const
{
    if (is_source_equal_dest_)
        return true;

    if (wgs84_to_merc_ || merc_to_wgs84_)
    {
        return backward(env);
    }

    std::vector<coord<double,2> > coords;
    envelope_points(coords, env, points);  // this is always clockwise

    double z;
    for (std::vector<coord<double,2> >::iterator it = coords.begin(); it!=coords.end(); ++it) {
        z = 0;
        if (!backward(it->x, it->y, z)) {
            return false;
        }
    }

    box2d<double> result = calculate_bbox(coords);
    if (is_source_longlat_ && !is_clockwise(coords))
    {
        // we've gone to a geographic CS, and our clockwise envelope has
        // changed into an anticlockwise one. This means we've crossed the antimeridian, and
        // need to expand the X direction to +/-180 to include all the data. Once we can deal
        // with multiple bboxes in queries we can improve.
        double miny = result.miny();
        result.expand_to_include(-180.0, miny);
        result.expand_to_include(180.0, miny);
    }

    env.re_center(result.center().x, result.center().y);
    env.height(result.height());
    env.width(result.width());

    return true;
}

bool proj_transform::forward(box2d<double>& env, int points) const
{
    if (is_source_equal_dest_)
        return true;

    if (wgs84_to_merc_ || merc_to_wgs84_)
    {
        return forward(env);
    }

    std::vector<coord<double,2> > coords;
    envelope_points(coords, env, points);  // this is always clockwise

    double z;
    for (std::vector<coord<double,2> >::iterator it = coords.begin(); it!=coords.end(); ++it) {
        z = 0;
        if (!forward(it->x, it->y, z)) {
            return false;
        }
    }

    box2d<double> result = calculate_bbox(coords);

    if (is_dest_longlat_ && !is_clockwise(coords))
    {
        // we've gone to a geographic CS, and our clockwise envelope has
        // changed into an anticlockwise one. This means we've crossed the antimeridian, and
        // need to expand the X direction to +/-180 to include all the data. Once we can deal
        // with multiple bboxes in queries we can improve.
        double miny = result.miny();
        result.expand_to_include(-180.0, miny);
        result.expand_to_include(180.0, miny);
    }

    env.re_center(result.center().x, result.center().y);
    env.height(result.height());
    env.width(result.width());

    return true;
}

mapnik::projection const& proj_transform::source() const
{
    return source_;
}
mapnik::projection const& proj_transform::dest() const
{
    return dest_;
}

}