1 /* ============================================================
2 * JRobin : Pure java implementation of RRDTool's functionality
3 * ============================================================
4 *
5 * Project Info: http://www.jrobin.org
6 * Project Lead: Sasa Markovic (saxon@jrobin.org)
7 *
8 * Developers: Sasa Markovic (saxon@jrobin.org)
9 *
10 *
11 * (C) Copyright 2003-2005, by Sasa Markovic.
12 *
13 * This library is free software; you can redistribute it and/or modify it under the terms
14 * of the GNU Lesser General Public License as published by the Free Software Foundation;
15 * either version 2.1 of the License, or (at your option) any later version.
16 *
17 * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
18 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
19 * See the GNU Lesser General Public License for more details.
20 *
21 * You should have received a copy of the GNU Lesser General Public License along with this
22 * library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
23 * Boston, MA 02111-1307, USA.
24 */
25 package org.jrobin.data;
26
27 import org.jrobin.core.RrdException;
28 import org.jrobin.core.Util;
29
30 import java.util.Calendar;
31 import java.util.Date;
32
33 /**
34 * Class used to interpolate datasource values from the collection of (timestamp, values)
35 * points. This class is suitable for linear interpolation only. <p>
36 * <p/>
37 * Interpolation algorithm returns different values based on the value passed to
38 * {@link #setInterpolationMethod(int) setInterpolationMethod()}. If not set, interpolation
39 * method defaults to standard linear interpolation ({@link #INTERPOLATE_LINEAR}).
40 * Interpolation method handles NaN datasource
41 * values gracefully.<p>
42 */
43 public class LinearInterpolator extends Plottable {
44 /**
45 * constant used to specify LEFT interpolation.
46 * See {@link #setInterpolationMethod(int) setInterpolationMethod()} for explanation.
47 */
48 public static final int INTERPOLATE_LEFT = 0;
49 /**
50 * constant used to specify RIGHT interpolation.
51 * See {@link #setInterpolationMethod(int) setInterpolationMethod()} for explanation.
52 */
53 public static final int INTERPOLATE_RIGHT = 1;
54 /**
55 * constant used to specify LINEAR interpolation (default interpolation method).
56 * See {@link #setInterpolationMethod(int) setInterpolationMethod()} for explanation.
57 */
58 public static final int INTERPOLATE_LINEAR = 2;
59 /**
60 * constant used to specify LINEAR REGRESSION as interpolation method.
61 * See {@link #setInterpolationMethod(int) setInterpolationMethod()} for explanation.
62 */
63 public static final int INTERPOLATE_REGRESSION = 3;
64
65 private int lastIndexUsed = 0;
66 private int interpolationMethod = INTERPOLATE_LINEAR;
67
68 private long[] timestamps;
69 private double[] values;
70
71 // used only if INTERPOLATE_BESTFIT is specified
72 double b0 = Double.NaN, b1 = Double.NaN;
73
74 /**
75 * Creates LinearInterpolator from arrays of timestamps and corresponding datasource values.
76 *
77 * @param timestamps timestamps in seconds
78 * @param values corresponding datasource values
79 * @throws RrdException Thrown if supplied arrays do not contain at least two values, or if
80 * timestamps are not ordered, or array lengths are not equal.
81 */
82 public LinearInterpolator(long[] timestamps, double[] values) throws RrdException {
83 this.timestamps = timestamps;
84 this.values = values;
85 validate();
86 }
87
88 /**
89 * Creates LinearInterpolator from arrays of timestamps and corresponding datasource values.
90 *
91 * @param dates Array of Date objects
92 * @param values corresponding datasource values
93 * @throws RrdException Thrown if supplied arrays do not contain at least two values, or if
94 * timestamps are not ordered, or array lengths are not equal.
95 */
96 public LinearInterpolator(Date[] dates, double[] values) throws RrdException {
97 this.values = values;
98 timestamps = new long[dates.length];
99 for (int i = 0; i < dates.length; i++) {
100 timestamps[i] = Util.getTimestamp(dates[i]);
101 }
102 validate();
103 }
104
105 /**
106 * Creates LinearInterpolator from arrays of timestamps and corresponding datasource values.
107 *
108 * @param dates array of GregorianCalendar objects
109 * @param values corresponding datasource values
110 * @throws RrdException Thrown if supplied arrays do not contain at least two values, or if
111 * timestamps are not ordered, or array lengths are not equal.
112 */
113 public LinearInterpolator(Calendar[] dates, double[] values) throws RrdException {
114 this.values = values;
115 timestamps = new long[dates.length];
116 for (int i = 0; i < dates.length; i++) {
117 timestamps[i] = Util.getTimestamp(dates[i]);
118 }
119 validate();
120 }
121
122 private void validate() throws RrdException {
123 boolean ok = true;
124 if (timestamps.length != values.length || timestamps.length < 2) {
125 ok = false;
126 }
127 for (int i = 0; i < timestamps.length - 1 && ok; i++) {
128 if (timestamps[i] >= timestamps[i + 1]) {
129 ok = false;
130 }
131 }
132 if (!ok) {
133 throw new RrdException("Invalid plottable data supplied");
134 }
135 }
136
137 /**
138 * Sets interpolation method to be used. Suppose that we have two timestamp/value pairs:<br>
139 * <code>(t, 100)</code> and <code>(t + 100, 300)</code>. Here are the results interpolator
140 * returns for t + 50 seconds, for various <code>interpolationMethods</code>:<p>
141 * <ul>
142 * <li><code>INTERPOLATE_LEFT: 100</code>
143 * <li><code>INTERPOLATE_RIGHT: 300</code>
144 * <li><code>INTERPOLATE_LINEAR: 200</code>
145 * </ul>
146 * If not set, interpolation method defaults to <code>INTERPOLATE_LINEAR</code>.<p>
147 * <p/>
148 * The fourth available interpolation method is INTERPOLATE_REGRESSION. This method uses
149 * simple linear regression to interpolate supplied data with a simple straight line which does not
150 * necessarily pass through all data points. The slope of the best-fit line will be chosen so that the
151 * total square distance of real data points from from the best-fit line is at minimum.<p>
152 * <p/>
153 * The full explanation of this inteprolation method can be found
154 * <a href="http://www.tufts.edu/~gdallal/slr.htm">here</a>.<p>
155 *
156 * @param interpolationMethod Should be <code>INTERPOLATE_LEFT</code>,
157 * <code>INTERPOLATE_RIGHT</code>, <code>INTERPOLATE_LINEAR</code> or
158 * <code>INTERPOLATE_REGRESSION</code>. Any other value will be interpreted as
159 * INTERPOLATE_LINEAR (default).
160 */
161 public void setInterpolationMethod(int interpolationMethod) {
162 switch (interpolationMethod) {
163 case INTERPOLATE_REGRESSION:
164 calculateBestFitLine();
165 case INTERPOLATE_LEFT:
166 case INTERPOLATE_RIGHT:
167 case INTERPOLATE_LINEAR:
168 this.interpolationMethod = interpolationMethod;
169 break;
170 default:
171 this.interpolationMethod = INTERPOLATE_LINEAR;
172 }
173 }
174
175 private void calculateBestFitLine() {
176 int count = timestamps.length, validCount = 0;
177 double ts = 0.0, vs = 0.0;
178 for (int i = 0; i < count; i++) {
179 if (!Double.isNaN(values[i])) {
180 ts += timestamps[i];
181 vs += values[i];
182 validCount++;
183 }
184 }
185 if (validCount <= 1) {
186 // just one not-NaN point
187 b0 = b1 = Double.NaN;
188 return;
189 }
190 ts /= validCount;
191 vs /= validCount;
192 double s1 = 0, s2 = 0;
193 for (int i = 0; i < count; i++) {
194 if (!Double.isNaN(values[i])) {
195 double dt = timestamps[i] - ts;
196 double dv = values[i] - vs;
197 s1 += dt * dv;
198 s2 += dt * dt;
199 }
200 }
201 b1 = s1 / s2;
202 b0 = vs - b1 * ts;
203 }
204
205 /**
206 * Method overriden from the base class. This method will be called by the framework. Call
207 * this method only if you need interpolated values in your code.
208 *
209 * @param timestamp timestamp in seconds
210 * @return inteprolated datasource value
211 */
212 public double getValue(long timestamp) {
213 if (interpolationMethod == INTERPOLATE_REGRESSION) {
214 return b0 + b1 * timestamp;
215 }
216 int count = timestamps.length;
217 // check if out of range
218 if (timestamp < timestamps[0] || timestamp > timestamps[count - 1]) {
219 return Double.NaN;
220 }
221 // find matching segment
222 int startIndex = lastIndexUsed;
223 if (timestamp < timestamps[lastIndexUsed]) {
224 // backward reading, shift to the first timestamp
225 startIndex = 0;
226 }
227 for (int i = startIndex; i < count; i++) {
228 if (timestamps[i] == timestamp) {
229 return values[i];
230 }
231 if (i < count - 1 && timestamps[i] < timestamp && timestamp < timestamps[i + 1]) {
232 // matching segment found
233 lastIndexUsed = i;
234 switch (interpolationMethod) {
235 case INTERPOLATE_LEFT:
236 return values[i];
237 case INTERPOLATE_RIGHT:
238 return values[i + 1];
239 case INTERPOLATE_LINEAR:
240 double slope = (values[i + 1] - values[i]) /
241 (timestamps[i + 1] - timestamps[i]);
242 return values[i] + slope * (timestamp - timestamps[i]);
243 default:
244 return Double.NaN;
245 }
246 }
247 }
248 // should not be here ever, but let's satisfy the compiler
249 return Double.NaN;
250 }
251 }