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111 lines
2.5 KiB
111 lines
2.5 KiB
/*
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* Copyright 2012, The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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//#define LOG_NDEBUG 0
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#define LOG_TAG "LinearRegression"
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#include <utils/Log.h>
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#include "include/LinearRegression.h"
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#include <math.h>
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#include <string.h>
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namespace android {
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LinearRegression::LinearRegression(size_t historySize)
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: mHistorySize(historySize),
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mCount(0),
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mHistory(new Point[mHistorySize]),
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mSumX(0.0),
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mSumY(0.0) {
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}
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LinearRegression::~LinearRegression() {
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delete[] mHistory;
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mHistory = NULL;
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}
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void LinearRegression::addPoint(float x, float y) {
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if (mCount == mHistorySize) {
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const Point &oldest = mHistory[0];
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mSumX -= oldest.mX;
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mSumY -= oldest.mY;
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memmove(&mHistory[0], &mHistory[1], (mHistorySize - 1) * sizeof(Point));
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--mCount;
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}
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Point *newest = &mHistory[mCount++];
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newest->mX = x;
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newest->mY = y;
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mSumX += x;
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mSumY += y;
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}
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bool LinearRegression::approxLine(float *n1, float *n2, float *b) const {
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static const float kEpsilon = 1.0E-4;
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if (mCount < 2) {
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return false;
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}
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float sumX2 = 0.0f;
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float sumY2 = 0.0f;
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float sumXY = 0.0f;
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float meanX = mSumX / (float)mCount;
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float meanY = mSumY / (float)mCount;
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for (size_t i = 0; i < mCount; ++i) {
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const Point &p = mHistory[i];
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float x = p.mX - meanX;
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float y = p.mY - meanY;
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sumX2 += x * x;
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sumY2 += y * y;
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sumXY += x * y;
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}
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float T = sumX2 + sumY2;
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float D = sumX2 * sumY2 - sumXY * sumXY;
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float root = sqrt(T * T * 0.25 - D);
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float L1 = T * 0.5 - root;
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if (fabs(sumXY) > kEpsilon) {
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*n1 = 1.0;
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*n2 = (2.0 * L1 - sumX2) / sumXY;
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float mag = sqrt((*n1) * (*n1) + (*n2) * (*n2));
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*n1 /= mag;
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*n2 /= mag;
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} else {
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*n1 = 0.0;
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*n2 = 1.0;
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}
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*b = (*n1) * meanX + (*n2) * meanY;
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return true;
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}
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} // namespace android
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