How can i get interpolated Polar coordinates? - c++

Question

I have a problem to get a discrete Sequence of a contour.
My idea: I want to place an anchor in a middle of a closed contour in an image and use polar coordinates to get a length for each degree of the polar coordinates.
I already have created a vector of fixed length 360 and iterate through all contour points(ca. 4000) with length l=contour.length/360. Here i get 360 values along the contour with length l. But i want to have a discrete value for each integer degree from 1 to 360.
Can i interpolate my array to fix values from 1 to 360?
vector<cv::Point> cn;
double theta = 0;
double dis = 0;
int polsize = 360;
int psize = 0;
for (int k = 0; k < cnts[0].size(); k++) {
cn.push_back(cnts[0].at(k));
}
double pstep = cn.size() / polsize;
for (int m = 1; m < polsize; m++) {
psize = (int)(m * pstep);
polar(cn[psize].x, cn[psize].y, &dis, &theta);
outputFile << theta << "/" << dis << ";";
}
void polar(int x, int y, double* r, double* theta)
{
double toDegrees = 180 / 3.141593;
*r = sqrt((pow(x, 2)) + (pow(y, 2)));
double xt = x, yt = y;
yt = 1024 - yt;
if (xt == 0) xt = 0.1;
if (yt == 0) yt = 0.1;
*theta = atan(yt / xt) * toDegrees;
if (*theta < 0) *theta = *theta+180;
return;
}

Answer 1

You seem to miss some of the C++ basics. E.g.
1) If you use at() you add unnecessary range checking. As you are looping until cnts[0].size() you're doing that twice now.
2) you don't need to use return in void functions.
3) don't use pointers for return. This is C++, not C. Use references, or std::tuple return type.
Then you're actually replicating the std::complex type.
The code can be really simple.
#include <vector>
//#include <algorithm> // if using std::copy
#include <cmath>
#include <sstream> // only for the temporary output.
static constexpr auto toDeg = 180 / 3.141593;
struct Point{
double x,y;
double abs() const {
return std::sqrt(std::pow(x,2) + std::pow(y,2));
}
double arg() const {
return std::atan2(y, x) * toDeg;
}
};
int main(){
std::vector<std::vector<Point>> cnts = {{{1,1}}};
// copy constructor
std::vector<Point> cn(cnts[0]);
// range-based constructor
//std::vector<Point> cn(std::cbegin(cnts[0]), std::cend(cnts[0]));
// or copy-insert
//std::vector<Point> cn
//cn.reserve(cnts[0].size());
//std::copy(std::cbegin(cnts[0]), std::cend(cnts[0]), std::back_inserter(cn));
std::stringstream outputFile; // temp
for (auto const& el : cn) {
outputFile << el.arg() << "/" << el.abs() << ";";
}
}