Subversion Repositories mkgmap

/*
 * Copyright (C) 2017.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 3 or
 * version 2 as published by the Free Software Foundation.
 *
 * This program 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
 * General Public License for more details.
 *
 * Author: Ticker Berkin
 * Create date: 27-Jan-2017
 */
package uk.me.parabola.mkgmap.filters;

import java.util.List;

import uk.me.parabola.imgfmt.app.Coord;

/**
 * Not actually a real filter, but estimates the number of points that would be left in
 * a polygon or line after simple RemoveObsolete/RoundCoords filtering at a given resolution
 *
 * Possibly could be extended to predict the effect of straight lines and spike removal
 * but wanted it to be as simple as possible to start with.
 *
 * @author Ticker Berkin
 */
public class PredictFilterPoints {

        public static int predictedMaxNumPoints(List<Coord> points, int resolution, boolean checkPreserved) {

                // see RemoveObsoletePointsFilter, RoundCoordsFilter, ... for comments on preserved and resolution
                // %%% checkPreserved = config.getLevel() == 0 && config.isRoutable() && line.isRoad()){
           
//              final int shift = 30 - resolution; // NB getting highPrec
//              final int half = 1 << (shift - 1); // 0.5 shifted
//              final int mask = ~((1 << shift) - 1); // to remove fraction bits
                final int shift = 24 - resolution; // best use same info as filters
                int half;
                int mask;
                if (shift == 0) {
                        half = 0;
                        mask = ~0;
                } else {
                        half = 1 << (shift - 1); // 0.5 shifted
                        mask = ~((1 << shift) - 1); // to remove fraction bits
                }

                int numPoints = 0;
                int lastLat = 0, lastLon = 0;
                for (Coord p : points) {
//                      final int lat = (p.getHighPrecLat() + half) & mask;
//                      final int lon = (p.getHighPrecLon() + half) & mask;
                        final int lat = (p.getLatitude() + half) & mask;
                        final int lon = (p.getLongitude() + half) & mask;
                        if (numPoints == 0)
                                numPoints = 1; // always have one/first point
                        else {
                                if (lat != lastLat || lon != lastLon || (checkPreserved && p.isNumberNode()))
                                        ++numPoints;
                        }
                        lastLat = lat;
                        lastLon = lon;
                }
                return numPoints; // true shapes will have >3 points, lines >1
        } // predictNumNumPoints

}