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GraphHopper is a fast and memory efficient Java road routing engine working seamlessly with OpenStreetMap data.
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/*
 *  Licensed to GraphHopper GmbH under one or more contributor
 *  license agreements. See the NOTICE file distributed with this work for
 *  additional information regarding copyright ownership.
 *
 *  GraphHopper GmbH licenses this file to you under the Apache License,
 *  Version 2.0 (the "License"); you may not use this file except in
 *  compliance with the License. You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package com.graphhopper.reader.dem;

import java.io.*;

import static com.graphhopper.util.Helper.*;

/**
 * SRTMGL1 contains elevation data for most of the world with 1 arc second (~30m) accuracy.
 * We use the mirror of OpenTopography, as the official SRTMGL1 download requires authentication.
 * http://opentopo.sdsc.edu/raster?opentopoID=OTSRTM.082015.4326.1
 * 
 * TODO: In addition, NSF requires oral acknowledgment during all news media interviews.
 * TODO: This is weird, we have to check if really want to use OpenTopography then, see: http://www.opentopography.org/citations
 * 

 * When using this data we have to acknowledge:
 * This material is based on data services provided by the OpenTopography Facility with support from the
 * National Science Foundation under NSF Award Numbers 1226353 & 1225810
 * National Geospatial-Intelligence Agency (NGA) and the National Aeronautics and Space Administration (NASA), 2013,
 * SRTMGL1: NASA Shuttle Radar Topography Mission Global 1 arc second V003. [Version]. NASA EOSDIS Land Processes DAAC,
 * USGS Earth Resources Observation and Science (EROS) Center, Sioux Falls, South Dakota (https://lpdaac.usgs.gov),
 * accessed 11 29, 2017, at https://doi.org/10.5067/measures/srtm/srtmgl1.003
 * 
 * Detailed information can be found here: https://lpdaac.usgs.gov/sites/default/files/public/measures/docs/NASA_SRTM_V3.pdf
 *
 * @author Robin Boldt
 */
public class SRTMGL1Provider extends AbstractSRTMElevationProvider {

    private final int latDegree = 1;
    private final int lonDegree = 1;

    public SRTMGL1Provider() {
        this("");
    }

    public SRTMGL1Provider(String cacheDir) {
        super("https://cloud.sdsc.edu/v1/AUTH_opentopography/Raster/SRTM_GL1/SRTM_GL1_srtm/",
                cacheDir.isEmpty() ? "/tmp/srtmgl1" : cacheDir,
                "GraphHopper SRTMReader",
                -56,
                60,
                3601
        );
    }

    public static void main(String[] args) throws IOException {
        SRTMGL1Provider provider = new SRTMGL1Provider();
        // 338
        System.out.println(provider.getEle(49.949784, 11.57517));
        // 468
        System.out.println(provider.getEle(49.968668, 11.575127));
        // 467
        System.out.println(provider.getEle(49.968682, 11.574842));
        // 3110
        System.out.println(provider.getEle(-22.532854, -65.110474));
        // 120
        System.out.println(provider.getEle(38.065392, -87.099609));
        // 1617
        System.out.println(provider.getEle(40, -105.2277023));
        System.out.println(provider.getEle(39.99999999, -105.2277023));
        System.out.println(provider.getEle(39.9999999, -105.2277023));
        System.out.println(provider.getEle(39.999999, -105.2277023));
        // 1015
        System.out.println(provider.getEle(47.468668, 14.575127));
        // 1107
        System.out.println(provider.getEle(47.467753, 14.573911));
        // 1930
        System.out.println(provider.getEle(46.468835, 12.578777));
        // 844
        System.out.println(provider.getEle(48.469123, 9.576393));
    }

    @Override
    byte[] readFile(File file) throws IOException {
        InputStream is = new FileInputStream(file);
        BufferedInputStream buff = new BufferedInputStream(is);
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        byte[] buffer = new byte[0xFFFF];
        int len;
        while ((len = buff.read(buffer)) > 0) {
            os.write(buffer, 0, len);
        }
        os.flush();
        close(buff);
        return os.toByteArray();
    }

    int getMinLatForTile(double lat) {
        return (int) (Math.floor((90 + lat) / latDegree) * latDegree) - 90;
    }

    int getMinLonForTile(double lon) {
        return (int) (Math.floor((180 + lon) / lonDegree) * lonDegree) - 180;
    }

    String getFileName(double lat, double lon) {
        int lonInt = getMinLonForTile(lon);
        int latInt = getMinLatForTile(lat);
        return toLowerCase(getNorthString(latInt) + getPaddedLatString(latInt) + getEastString(lonInt) + getPaddedLonString(lonInt));
    }

    String getDownloadURL(double lat, double lon) {
        int lonInt = getMinLonForTile(lon);
        int latInt = getMinLatForTile(lat);
        String north = getNorthString(latInt);
        String dir;
        if (north.equals("N")) {
            dir = "North/";
            if (lat >= 30)
                dir += "North_30_60/";
            else
                dir += "North_0_29/";
        } else {
            dir = "South/";
        }

        return dir + north + getPaddedLatString(latInt) + getEastString(lonInt) + getPaddedLonString(lonInt) + ".hgt";
    }

    private String getNorthString(int lat) {
        if (lat < 0) {
            return "S";
        }
        return "N";
    }

    private String getEastString(int lon) {
        if (lon < 0) {
            return "W";
        }
        return "E";
    }

    @Override
    public String toString() {
        return "srtmgl1";
    }

}