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mapnik/include/mapnik/markers_placement.hpp

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/*****************************************************************************
*
* This file is part of Mapnik (c++ mapping toolkit)
*
* Copyright (C) 2011 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
*
*****************************************************************************/
#ifndef MAPNIK_MARKERS_PLACEMENT_HPP
#define MAPNIK_MARKERS_PLACEMENT_HPP
// agg
#include "agg_basics.h"
// mapnik
#include <mapnik/box2d.hpp>
// boost
#include <boost/utility.hpp>
// stl
#include <cmath>
namespace mapnik {
template <typename Locator, typename Detector>
class markers_placement : boost::noncopyable
{
public:
markers_placement(Locator &locator, box2d<double> size, Detector &detector, double spacing, double max_error, bool allow_overlap);
void rewind();
bool get_point(double *x, double *y, double *angle, bool add_to_detector = true);
private:
Locator &locator_;
box2d<double> size_;
Detector &detector_;
double spacing_;
bool done_;
double last_x, last_y;
double next_x, next_y;
/** If a marker could not be placed at the exact point where it should
* go the next markers distance will be a bit lower. */
double error_;
double max_error_;
unsigned marker_nr_;
bool allow_overlap_;
box2d<double> perform_transform(double angle, double dx, double dy);
double find_optimal_spacing(double s);
};
/** Constructor for markers_placement object.
* \param locator Path along which markers are placed (type: vertex source)
* \param size Size of the marker
* \param detector Collision detection
* \param spacing Distance between markers. If the value is negative it is
* converted to a positive value with similar magnitude, but
* choosen to optimize marker placement. 0 = no markers
*/
template <typename Locator, typename Detector> markers_placement<Locator, Detector>::markers_placement(
Locator &locator, box2d<double> size, Detector &detector, double spacing, double max_error, bool allow_overlap)
: locator_(locator), size_(size), detector_(detector), max_error_(max_error), allow_overlap_(allow_overlap)
{
if (spacing >= 0)
{
spacing_ = spacing;
} else if (spacing < 0)
{
spacing_ = find_optimal_spacing(-spacing);
}
rewind();
}
/** Autmatically chooses spacing. */
template <typename Locator, typename Detector> double markers_placement<Locator, Detector>::find_optimal_spacing(double s)
{
rewind();
//Calculate total path length
unsigned cmd = agg::path_cmd_move_to;
double length = 0;
while (!agg::is_stop(cmd))
{
double dx = next_x - last_x;
double dy = next_y - last_y;
length += std::sqrt(dx * dx + dy * dy);
last_x = next_x;
last_y = next_y;
while (agg::is_move_to(cmd = locator_.vertex(&next_x, &next_y)))
{
//Skip over "move" commands
last_x = next_x;
last_y = next_y;
}
}
unsigned points = round(length / s);
if (points == 0) return 0; //Path to short
return length / points;
}
/** Start again at first marker.
* \note Returning the same list of markers only works when they were NOT added
* to the detector.
*/
template <typename Locator, typename Detector> void markers_placement<Locator, Detector>::rewind()
{
locator_.rewind(0);
//Get first point
done_ = agg::is_stop(locator_.vertex(&next_x, &next_y)) || spacing_ < size_.width();
last_x = next_x;
last_y = next_y; // Force request of new segment
error_ = 0;
marker_nr_ = 0;
}
/** Get a point where the marker should be placed.
* Each time this function is called a new point is returned.
* \param x Return value for x position
* \param y Return value for x position
* \param angle Return value for rotation angle
* \param add_to_detector Add selected position to detector
* \return True if a place is found, false if none is found.
*/
template <typename Locator, typename Detector> bool markers_placement<Locator, Detector>::get_point(
double *x, double *y, double *angle, bool add_to_detector)
{
if (done_) return false;
unsigned cmd;
double spacing_left;
if (marker_nr_++ == 0)
{
spacing_left = spacing_ / 2;
} else
{
spacing_left = spacing_;
}
spacing_left -= error_;
error_ = 0;
while (true)
{
//Loop exits when a position is found or when no more segments are available
if (spacing_left < size_.width()/2)
{
//Do not place markers to close to the beginning of a segment
error_ += size_.width()/2 - spacing_left;
spacing_left = size_.width()/2;
}
if (abs(error_) > max_error_ * spacing_)
{
spacing_left += spacing_ - error_;
error_ = 0;
}
double dx = next_x - last_x;
double dy = next_y - last_y;
double d = std::sqrt(dx * dx + dy * dy);
if (d <= spacing_left)
{
//Segment is to short to place marker. Find next segment
spacing_left -= d;
last_x = next_x;
last_y = next_y;
while (agg::is_move_to(cmd = locator_.vertex(&next_x, &next_y)))
{
//Skip over "move" commands
last_x = next_x;
last_y = next_y;
}
if (agg::is_stop(cmd))
{
done_ = true;
return false;
}
continue; //Try again
}
//Check if marker really fits in this segment
if (d < size_.width())
{
//Segment to short => Skip this segment
error_ += d + size_.width()/2 - spacing_left;
spacing_left = d + size_.width()/2;
continue;
} else if (d - spacing_left < size_.width()/2)
{
//Segment is long enough, but we are to close to the end
//Note: This function moves backwards. This could lead to an infinite
// loop when another function adds a positive offset. Therefore we
// only move backwards when there is no offset
if (error_ == 0)
{
error_ += d - size_.width()/2 - spacing_left;
spacing_left = d - size_.width()/2;
} else
{
//Skip this segment
error_ += d + size_.width()/2 - spacing_left;
spacing_left = d + size_.width()/2;
}
continue; //Force checking of max_error constraint
}
*angle = atan2(dy, dx);
*x = last_x + dx * (spacing_left / d);
*y = last_y + dy * (spacing_left / d);
box2d<double> box = perform_transform(*angle, *x, *y);
if (!allow_overlap_ && !detector_.has_placement(box))
{
//10.0 is choosen arbitrarily
error_ += spacing_ * max_error_ / 10.0;
spacing_left += spacing_ * max_error_ / 10.0;
continue;
}
if (add_to_detector) detector_.insert(box);
last_x = *x;
last_y = *y;
return true;
}
}
/** Rotates the size_ box and translates the position. */
template <typename Locator, typename Detector> box2d<double> markers_placement<Locator, Detector>::perform_transform(double angle, double dx, double dy)
{
double c = cos(angle), s = sin(angle);
double x1 = size_.minx();
double x2 = size_.maxx();
double y1 = size_.miny();
double y2 = size_.maxy();
double x1_ = dx + x1 * c - y1 * s;
double y1_ = dy + x1 * s + y1 * c;
double x2_ = dx + x2 * c - y2 * s;
double y2_ = dy + x2 * s + y2 * c;
return box2d<double>(x1_, y1_, x2_, y2_);
}
}
#endif // MAPNIK_MARKERS_PLACEMENT_HPP
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