LibSimpleFilters/MedianFilter.h at master · arc12/LibSimpleFilters · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
/* MedianFilter.h - Median Filter
 Copyright 2012, Adam Cooper */

/* ***************************** LICENCE ************************************
 *  This file is part of LibSimpleFilters Arduino library.                   *
 *    (each component of the library is licenced separately)                 *
 *                                                                           *
 * MedianFilter 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 3 of the License, or      *
 * (at your option) any later version.                                       *
 *                                                                           *
 * 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 Lesser General Public License for more details.                       *
 *                                                                           *
 * You should have received a copy of the GNU Lesser General Public License  *
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.     *
 ****************************************************************************/
#ifndef MEDIAN_FILTER_H
#define MEDIAN_FILTER_H

#include "Arduino.h"

#define MEDIAN_MAX_LEN 25 //!< Maximum number of samples, as specified by the length parameter in the constructor. Absolute max is 256.

/*!  This filter calculates the median of a set number of previous values.
This is able to suppress sudden impules/glitches while still allowing step changes to be preserved, although delayed.
Longer buffers will reject longer outlier signals.\n
See http://en.wikipedia.org/wiki/Median_filter (also http://medim.sth.kth.se/6l2872/F/F7-1.pdf)\n
 To use: create an instance of the filter and submit new readings using update().
 Readings should be sampled at regular (i.e. equal) time intervals.
 @brief  A finite length median filter. */
class MedianFilter{
public:
  /*! Create the filter with specified parameters.
   @param length The number of samples to take into account with a maximum specified by MEDIAN_MAX_LEN. This should be odd; even values will be siltently increased by 1.
   @param burnIn Whether to initialise the filter on first reading such that the output = the input after that reading.
   Otherwise the output is as if the input had just been turned on with previous zero readings. */
  MedianFilter(int length, boolean burnIn);

  /*! Submit a new measurement to the filter.\n
  Readings should be sampled at regular (i.e. equal) time intervals.
   @param newVal The new value.
   @returns The filter output. */
  int update(int newVal);

  /*! Get the previously-submitted values. This is a "circular buffer" so the current pointer must be obtained using getLastIndex()
  @param[out] values A buffer of length specified by the length parameter in the constructor. */
  void getHistory(int values[]);
  /*! What was the last index used in the returned buffer from getHistory()?
  @returns The index to the value submitted by the last update() */
  int getLastIndex();

private:
  //constructor parameters
  boolean _burnIn;
  int _length;

  boolean _updated;//has the filter received any data yet
  int _values[MEDIAN_MAX_LEN];
  byte _sortList[MEDIAN_MAX_LEN]; //sorted order of entries in _values
  int _index;// pointer into _values[]

  //common code used by both update() methods
  void accumulate(int newVal);

};

#endif