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org.locationtech.proj4j.datum.NTV1 Maven / Gradle / Ivy
/*******************************************************************************
* Copyright 2009, 2017 Martin Davis
*
* Licensed 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 org.locationtech.proj4j.datum;
import static org.locationtech.proj4j.util.ProjectionMath.DTR;
import java.io.DataInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import org.locationtech.proj4j.util.FloatPolarCoordinate;
import org.locationtech.proj4j.util.IntPolarCoordinate;
import org.locationtech.proj4j.util.PolarCoordinate;
public final class NTV1 {
private static final byte[] magic1 = "HEADER".getBytes(StandardCharsets.US_ASCII);
private static final byte[] magic2 = "W GRID".getBytes(StandardCharsets.US_ASCII);
private static final byte[] magic3 = "TO NAD83 ".getBytes(StandardCharsets.US_ASCII);
public static boolean testHeader(byte[] header) {
return containsAt(magic1, header, 0) &&
containsAt(magic2, header, 96) &&
containsAt(magic3, header, 144);
}
public static Grid.ConversionTable init(DataInputStream definition) throws IOException {
byte[] header = new byte[160];
definition.readFully(header);
if (!testHeader(header)) throw new Error("Not a NTV1 file");
// Minimal validation to detect corrupt structure
int recordCount = intFromBytes(header, 8);
if (recordCount != 12) {
throw new Error(String.format("NTv1 grid shift file has wrong record count, corrupt? $0%08X $0", recordCount));
}
Grid.ConversionTable table = new Grid.ConversionTable();
table.id = "NTv1 Grid Shift File";
table.ll = new PolarCoordinate(-doubleFromBytes(header, 72), doubleFromBytes(header, 24));
PolarCoordinate ur = new PolarCoordinate(-doubleFromBytes(header, 56), doubleFromBytes(header, 40));
table.del = new PolarCoordinate(doubleFromBytes(header, 104), doubleFromBytes(header, 88));
table.lim = new IntPolarCoordinate(
(int) (Math.abs(ur.lam - table.ll.lam) / table.del.lam + 0.5) + 1,
(int) (Math.abs(ur.phi - table.ll.phi) / table.del.phi + 0.5) + 1);
table.ll.lam *= DTR;
table.ll.phi *= DTR;
table.del.lam *= DTR;
table.del.phi *= DTR;
return table;
}
public static void load(DataInputStream definition, Grid grid) throws IOException {
definition.skip(176);
double[] row_buff = new double[grid.table.lim.lam * 2];
FloatPolarCoordinate[] tmp_cvs =
new FloatPolarCoordinate[grid.table.lim.lam * grid.table.lim.phi];
for (int row = 0; row < grid.table.lim.phi; row++) {
byte[] byteBuff = new byte[8 * row_buff.length];
definition.readFully(byteBuff);
ByteBuffer.wrap(byteBuff).order(ByteOrder.BIG_ENDIAN).asDoubleBuffer().get(row_buff);
for (int i = 0; i < grid.table.lim.lam; i++) {
tmp_cvs[row * grid.table.lim.lam + grid.table.lim.lam - i - 1] =
new FloatPolarCoordinate(
(float) (row_buff[2 * i] * Math.PI / 180.0 / 3600.0),
(float) (row_buff[2 * i + 1] * Math.PI / 180.0 / 3600.0));
}
}
grid.table.cvs = tmp_cvs;
}
private static boolean containsAt(byte[] needle, byte[] haystack, int offset) {
if (needle == null || haystack == null) return false;
int maxoffset = Math.min(needle.length - 1, haystack.length - offset - 1);
for (int i = 0; i < maxoffset; i++) {
if (needle[i] != haystack[offset + i]) return false;
}
return true;
}
private static double doubleFromBytes(byte[] b, int offset) {
return ByteBuffer.wrap(b, offset, 8).order(ByteOrder.BIG_ENDIAN).getDouble();
}
private static int intFromBytes(byte[] b, int offset) {
return ByteBuffer.wrap(b, offset, 4).order(ByteOrder.BIG_ENDIAN).getInt();
}
}