LineEquation.cpp

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#include "LineEquation.h"
#include "IException.h"
#include "IString.h"
#include <iostream>
#include <iomanip>

using namespace std;

namespace Isis {
  LineEquation::LineEquation() {
    p_defined = false;
    p_slopeDefined = false;
    p_interceptDefined = false;
  }

  LineEquation::LineEquation(double x1, double y1, double x2, double y2) {
    p_defined = false;
    p_slopeDefined = false;
    p_interceptDefined = false;
    AddPoint(x1, y1);
    AddPoint(x2, y2);
    p_defined = true;
    p_slope = Slope();
    p_intercept = Intercept();
  }

  void LineEquation::AddPoint(double x, double y) {
    if(p_defined) {
      std::string msg = "Line equation is already defined with 2 points";
      throw IException(IException::Io, msg, _FILEINFO_);
    }
    p_x.push_back(x);
    p_y.push_back(y);
    if(Points() == 2) p_defined = true;
  }

  double LineEquation::Slope() {
    if(!p_defined) {
      std::string msg = "Line equation undefined:  2 points are required";
      throw IException(IException::Io, msg, _FILEINFO_);
    }
    else if(p_x[0] == p_x[1]) {
      std::string msg = "Points have identical independent variables -- no slope";
      throw IException(IException::Io, msg, _FILEINFO_);
    }
    else if(!p_slopeDefined) {
      p_slope = (p_y[0] - p_y[1]) / (p_x[0] - p_x[1]);
      p_slopeDefined = true;
    }
    return p_slope;
  }

  double LineEquation::Intercept() {
    if(!p_defined) {
      std::string msg = "Line equation undefined:  2 points are required";
      throw IException(IException::Io, msg, _FILEINFO_);
    }
    else if(p_x[0] == p_x[1]) {
      std::string msg = "Points have identical independent variables -- no intercept";
      throw IException(IException::Io, msg, _FILEINFO_);
    }
    else if(!p_interceptDefined) {
      p_intercept = p_y[0] - Slope() * p_x[0];
      p_interceptDefined = true;
    }

    return p_intercept;
  }

}