| /* |
| * Copyright 2012, The Android Open Source Project |
| * |
| * 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. |
| */ |
| |
| //#define LOG_NDEBUG 0 |
| #define LOG_TAG "LinearRegression" |
| #include <utils/Log.h> |
| |
| #include "LinearRegression.h" |
| |
| #include <math.h> |
| #include <string.h> |
| |
| namespace android { |
| |
| LinearRegression::LinearRegression(size_t historySize) |
| : mHistorySize(historySize), |
| mCount(0), |
| mHistory(new Point[mHistorySize]), |
| mSumX(0.0), |
| mSumY(0.0) { |
| } |
| |
| LinearRegression::~LinearRegression() { |
| delete[] mHistory; |
| mHistory = NULL; |
| } |
| |
| void LinearRegression::addPoint(float x, float y) { |
| if (mCount == mHistorySize) { |
| const Point &oldest = mHistory[0]; |
| |
| mSumX -= oldest.mX; |
| mSumY -= oldest.mY; |
| |
| memmove(&mHistory[0], &mHistory[1], (mHistorySize - 1) * sizeof(Point)); |
| --mCount; |
| } |
| |
| Point *newest = &mHistory[mCount++]; |
| newest->mX = x; |
| newest->mY = y; |
| |
| mSumX += x; |
| mSumY += y; |
| } |
| |
| bool LinearRegression::approxLine(float *n1, float *n2, float *b) const { |
| static const float kEpsilon = 1.0E-4; |
| |
| if (mCount < 2) { |
| return false; |
| } |
| |
| float sumX2 = 0.0f; |
| float sumY2 = 0.0f; |
| float sumXY = 0.0f; |
| |
| float meanX = mSumX / (float)mCount; |
| float meanY = mSumY / (float)mCount; |
| |
| for (size_t i = 0; i < mCount; ++i) { |
| const Point &p = mHistory[i]; |
| |
| float x = p.mX - meanX; |
| float y = p.mY - meanY; |
| |
| sumX2 += x * x; |
| sumY2 += y * y; |
| sumXY += x * y; |
| } |
| |
| float T = sumX2 + sumY2; |
| float D = sumX2 * sumY2 - sumXY * sumXY; |
| float root = sqrt(T * T * 0.25 - D); |
| |
| float L1 = T * 0.5 - root; |
| |
| if (fabs(sumXY) > kEpsilon) { |
| *n1 = 1.0; |
| *n2 = (2.0 * L1 - sumX2) / sumXY; |
| |
| float mag = sqrt((*n1) * (*n1) + (*n2) * (*n2)); |
| |
| *n1 /= mag; |
| *n2 /= mag; |
| } else { |
| *n1 = 0.0; |
| *n2 = 1.0; |
| } |
| |
| *b = (*n1) * meanX + (*n2) * meanY; |
| |
| return true; |
| } |
| |
| } // namespace android |
| |