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access single element in vec3d

Glaucous (24)
I have this code that store 3d coordinates in vec3d.
Now I am trying to find the average of max & min value in first column (which is c in my vec3d)
then let the z (third column in my vec3d), z = current x - (avg found)

I am having error with the following code to find max and min values.
E0349 no operator "<" matches these operands
C2678 binary '<': no operator found which takes a left-hand operand of type 'const cv::Vec3d' (or there is no acceptable conversion)
I tried to search to resolve the error but nothing helps.
I learn how to access 3 elements like, myVec.at(100), but I am having trouble to access a single element out from 3 values because it only making sense to me that now the vec3d comes in three. 

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#include "stdafx.h"
#include <opencv2/opencv.hpp>
#include "opencv2/core/core.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "iostream"
#include <vector>
#include <direct.h>
#include <algorithm> // for copy
#include <iterator> // for ostream_iterator

using namespace cv;
using namespace std;

Mat pic, gray, bw;
int rows, cols;

string path_in = "C:/Users/Dell/Desktop/";
string path_out = "C:/Users/Dell/Desktop/New Folder/";

/*bool sortcol(const myVec& v1,
const myVec& v2,
const myVec& v3)
{
return v1[1] < v2[1] < v3[1];
}*/

bool sortcol(const vector<Vec3d>& v1,
	const vector<Vec3d>& v2,
	const vector<Vec3d>& v3)
{
	return v1[1] < v2[1] < v3[1];
}

int main(int argc, char** argv)
{
	vector<cv::String> fn;
	vector<cv::String> fo;
	glob(path_in + "*.jpg", fn, false);
	glob(path_out + "*.jpg", fo, false);

	size_t count = fn.size();
	for (size_t i = 0; i < 1; i++) //try for an image first, if works, then try for all images in folder
	{
		pic = imread(fn[i], CV_LOAD_IMAGE_COLOR);
		cout << fn[i] << endl;

		cvtColor(pic, gray, CV_BGR2GRAY);
		//Canny(gray, gray, 50, 150, 3);

		threshold(gray, bw, 128.0, 255.0, THRESH_BINARY);

		std::vector<Vec3d> myVec;
		for (int r = 0; r < bw.rows; r++)
		{
			for (int c = 0; c < bw.cols; c++)
			{
				if (bw.at<uchar>(r, c) > 0) // white pixels
				{
					double z = 3.1209;
					//myVec.push_back(Point(r, c));
					myVec.push_back(Vec3d(c, r, z)); //add them to vector3d

					//cout << " : " << myVec.at<Vec3d>myVec.r << " , " << myVec.at<Vec3d>myVec.c << " , " << z << endl;
				}
			}
		}


		std::copy(myVec.begin(), myVec.end(), std::ostream_iterator<Vec3d>(std::cout << " " << std::endl));
		std::cout << "size: " << myVec.size() << '\n';
		//std::cout <<  myVec.at(myVec.size() - 1);
		//std::cout << ' ' << myVec.at(100) << '\n';

		//sort(myVec.begin(), myVec.end(), sortcol);
		auto min = std::min_element(myVec.begin(), myVec.end(), sortcol);
		auto max = std::max_element(myVec.begin(), myVec.end(), sortcol);


		waitKey(0);
	}

	system("PAUSE");
	//return 0;
}



Thank you .
tpb (1495)
Your sortcol is wrong. It isn't going to be passed three vectors. It's going to be passed two elements, which are Vec3d objects. So maybe something like this:
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bool sortcol(const Vec3d& v, const Vec3d& w)
{
    return v[1] < w[1];
}

It was complaining about the < sign because you were trying to compare two vectors instead of two doubles.
Last edited on
Glaucous (24)
Hi @tpb,

Thank you!

Is that mean 'v' and 'w' here are not vector?
Correct me if I am wrong, is v[1] < w[1] means that sort first column by comparing 1st element and second element, then second element with third element in the single column?

May I know how do i get single element from the first column ?
because they seems like come in three, i do not know how to get a single value?

or would you have any recommend reading materials you figured i shall go through to get that?
I think I might overlooked, or i just do not know the right keyword to look for.

Thanks again
Last edited on
icy1 (596)
Glacous, Vec3d appears to be a custom container of three doubles, as per the OpenCV documentation that I linked in the last post. v[1] is the second element in the v, likely equal to "y" coordinate.

Now I am trying to find the average of max & min value in first column

Not sure exactly what you're looking for. Here is an example which may give you some ideas:

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#include <iostream>
#include <array>
#include <vector>
#include <algorithm>

using namespace std;

// Similar to Vec3d
typedef array<double,3> Vec3d;

// From a collection of points, finds average coordinate value
//  i=0 - average X value
//  i=1 - average Y value
//  i=2 - average Z value
double AverageCoordinate(const vector<Vec3d>& v, int i)
{
    double sum = 0.0;
    for (auto& v3d : v)
        sum += v3d[i];
    return sum/v.size();
}

Vec3d AveragePoint(const Vec3d& a, const Vec3d& b)
{
    Vec3d avg;
    avg[0] = (a[0]+b[0])/2.0;
    avg[1] = (a[1]+b[1])/2.0;
    avg[2] = (a[2]+b[2])/2.0;
    return avg;
}

// From a collection of points, compare based on X, then Y, then Z
bool PointComparer(const Vec3d& a, const Vec3d& b)
{
    if (a[0] < b[0]) return true;
    if (a[0] > b[0]) return false;
    
    if (a[1] < b[1]) return true;
    if (a[1] > b[1]) return false;
    
    return a[2] < b[2];
}

void ShowPoint(const Vec3d& p)
{
    cout << "[" << p[0] << ", " << p[1] << ", " << p[2] << "]\n";
}

void Show(const vector<Vec3d>& v)
{
    for(auto& p : v)
        ShowPoint(p);
}

int main() 
{
    vector<Vec3d> points = 
    {
        {0.0, 0.4, 0.7},
        {0.2, 0.3, 0.0},
        {0.1, 0.7, 0.2},
        {0.7, 0.3, 0.5},
        {0.7, 0.2, 0.6},
        {0.9, 0.5, 0.4},
        {0.3, 0.2, 0.7},
        {0.8, 0.2, 0.2},
        {1.0, 0.8, 0.7},
        {0.8, 0.5, 0.0},
        {0.4, 0.7, 0.4},
        {0.0, 1.0, 0.0},
        {0.6, 0.8, 0.4},
        {0.4, 0.9, 0.6},
        {0.8, 0.0, 0.2},
        {0.6, 1.0, 0.1},
        {0.9, 0.3, 0.3},
        {0.9, 0.9, 0.0},
        {0.6, 0.5, 0.0},
        {0.9, 0.6, 0.3},
        {0.4, 0.2, 0.4},
        {0.9, 0.3, 0.6},
        {0.3, 0.6, 0.5},
        {0.8, 0.9, 0.7},
        {0.0, 0.6, 0.2},
        {0.1, 0.8, 0.3},
        {0.7, 0.8, 0.7},
        {0.7, 0.6, 0.0},
        {0.6, 0.5, 0.3},
        {0.4, 0.6, 0.0},
        {0.9, 0.5, 0.9},
        {0.2, 1.0, 0.6},
        {1.0, 0.2, 0.0},
        {0.1, 0.8, 0.8},
        {0.1, 0.8, 0.7},
        {0.3, 0.2, 0.4},
        {0.4, 0.0, 0.4},
        {0.9, 0.5, 0.0},
        {0.4, 0.4, 0.4},
        {0.9, 0.2, 0.3},
        {0.6, 0.6, 0.1},
        {0.7, 0.7, 0.2},
        {0.9, 0.8, 0.2},
        {0.2, 0.7, 0.2},
        {0.3, 0.1, 0.6},
        {1.0, 0.7, 0.0},
        {0.0, 0.2, 0.4},
        {0.1, 0.7, 0.0},
        {0.0, 1.0, 0.1},
        {0.8, 0.3, 0.2},
        {0.0, 0.3, 1.0},
        {0.2, 0.5, 1.0},
        {0.7, 0.1, 0.1},
        {0.3, 1.0, 0.9},
        {0.0, 0.0, 0.6},
        {0.9, 0.0, 0.3},
        {0.3, 0.3, 0.3},
        {0.1, 0.6, 0.3},
        {0.0, 0.9, 0.7},
        {1.0, 0.1, 0.5},
        {0.0, 1.0, 1.0},
        {0.4, 0.6, 0.9},
        {0.9, 0.8, 0.0},
        {0.3, 0.9, 0.9},
        {0.4, 0.4, 0.1},
        {0.9, 0.3, 0.7},
        {0.4, 0.7, 0.5},
        {0.1, 1.0, 0.8},
        {0.2, 0.2, 0.7},
        {0.8, 1.0, 0.6},
        {0.6, 0.1, 0.5},
        {0.8, 0.7, 1.0},
        {0.9, 0.9, 0.0},
        {0.1, 0.7, 0.7},
        {0.8, 1.0, 0.5},
        {0.0, 0.6, 0.8},
        {0.6, 1.0, 0.1},
        {0.6, 0.7, 0.2},
        {0.7, 0.6, 0.1},
        {0.5, 0.9, 0.3},
        {0.1, 1.0, 1.0},
        {0.4, 0.5, 0.3},
        {0.8, 0.9, 0.8},
        {0.6, 0.9, 0.1},
        {0.3, 0.7, 0.3},
        {0.2, 0.1, 0.8},
        {0.9, 0.3, 0.9},
        {0.6, 0.0, 0.3},
        {0.8, 0.4, 0.2},
        {0.9, 0.1, 0.6},
        {0.3, 0.5, 0.0},
        {0.5, 0.5, 0.1},
        {0.4, 0.6, 0.2},
        {1.0, 0.5, 0.0},
        {0.2, 1.0, 0.8},
        {0.8, 0.8, 0.9},
        {0.3, 0.2, 0.7},
        {0.8, 0.6, 0.3},
        {0.1, 0.0, 1.0},
        {0.8, 0.7, 0.9}
    };
    
    cout << "Before:" << endl;
    Show(points);
    cout << endl;
    
    cout << "After:" << endl;
    sort(points.begin(), points.end(), PointComparer);
    Show(points);
    
    cout << endl;
    cout << "AveragePoint of points[0] and points["<<points.size()-1<<"]:" << endl;
    ShowPoint(AveragePoint(points[0], points[points.size()-1]));
    
    cout << endl;
    cout << "AverageCoordinate from all points." << endl;
    cout << "  X: " << AverageCoordinate(points, 0) << endl;
    cout << "  Y: " << AverageCoordinate(points, 1) << endl;
    cout << "  Z: " << AverageCoordinate(points, 2) << endl;
    
    return 0;
}


can test at https://repl.it/repls/MeanGigaClosedsource
Last edited on
Glaucous (24)
Thank you so much icy1 ! below is my modified code referring your advised code

I have a doubt, may I know is the storing container now a vector or an array?
I am sorry, I am a little confused.
Sorry for the long-winded post. I have a few questions.

1. As I go through some sites, I figured tydef is like..
typedef existing_dataType<userDefined_dataType, numberInOneElement> storage_name;
is it correct??
typedef array<double, 3> cvVec3d;

2. I have a few comments listed in my code based on my weak assumptions.
Would you have a look and point it out if it is wrong?
Thank you so much.
It was so lovely wake up to this helpful code.

3. since 3 points together is An Element.
This is the first element in your code, [0, 0.4, 0.7],
If I were to refer 0.4, should I call it a point?
like "pointY in first element of Point (array/vector)" ?

4. Is it possible to have hundred of vector?
Like one vector per image? because sometimes i have up to 400 images.
I tried to make it like the below, but it seems that it doesn't work this way,
std::vector<Vec3d> myVec[i]; //i is the integer in image loop
but it says 'the value in variable i cannot be used as a constant'.

5. last question,
Am I able to retrieve single point out from an element?
[0, 0.4, 0.7], I want to get 0, so it is supposed to be a[0] or p[0],
so I tried to do the below, but it says, a and p are undefined?
cout << a[0] << endl;
cout << p[0] << endl;

I tried to change 'return avg' to 'return avg[0]' since I am only concern about the average of X.
but instead of getting 0.5, I got [0.5, 0, 0] :(

*p/s : I am actually need to generate z (third column value) from it respective x value. **with hope


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#include "stdafx.h"
#include <opencv2/opencv.hpp>
#include "opencv2/core/core.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "iostream"
#include <array>
#include <vector>
#include <direct.h>
#include <algorithm> // for copy
#include <iterator> // for ostream_iterator

using namespace cv;
using namespace std;

//if I put 'Vec3d' instead of 'cvVec3d', 
//it makes the rest of the Vec3d ambiguous.
// I know it has to do with the 'using namespace cv' above, 
//but I couldn't figured out why it's affected tho
//typedef existing_dataType<userDefined_dataType, numberInOneElement> storage_name;
typedef array<double, 3> cvVec3d; 

Mat pic, gray, bw;
int rows, cols;

//string path_in = "C:/Users/Dell/Desktop/";
//string path_out = "C:/Users/Dell/Desktop/New Folder/";

Vec3d AveragePoint(const Vec3d& a, const Vec3d& b) //comparing 2 elements
{
	Vec3d avg;

	//XYZ = 0,1,2 ; a=first entry in col, b=last entry in col
	avg[0] = (a[0] + b[0]) / 2.0; //X avg of max+min = first + last entry in the column
	avg[1] = (a[1] + b[1]) / 2.0; //Y avg of max+min
	avg[2] = (a[2] + b[2]) / 2.0; //Z avg of max+min
	return avg;
}

bool PointComparer(const Vec3d& a, const Vec3d& b) //comparing each value in column
{
	if (a[0] < b[0]) return true;  //sort from first to last point in X? true, if it is in ascending order
	if (a[0] > b[0]) return false;  //else

	if (a[1] < b[1]) return true;  //sort from first to last point in Y?
	if (a[1] > b[1]) return false;  //

	return a[2] <= b[2];  //compare first and last point in Z?
	//wonder why in this condition <= is used unlike the previous comparison with only < or > ?
}

void ShowPoint(const Vec3d& p) //show all points of particular element in array/vector
{
	cout << "[" << p[0] << ", " << p[1] << ", " << p[2] << "]\n"; 
}

void Show(const vector<Vec3d>& v)//show all points of all elements in array/vector
{
	//auto& modify values in sequence
	
	for (auto& p : v) //loop each element in v(vector in code)? while v is the total number in array/vector
		ShowPoint(p);
}

//attempts
/*bool sortcol(const myVec& v1,
const myVec& v2,
const myVec& v3)
{
return v1[1] < v2[1] < v3[1];
}*/

/*
bool sortcol(const Vec3d& v1,
	const Vec3d& v2)
{
	return v1[1] < v2[1];
}
*/

int main(int argc, char** argv)
{
	vector<cv::String> fn;
	vector<cv::String> fo;
	glob(path_in + "*.jpg", fn, false);
	glob(path_out + "*.jpg", fo, false);

	size_t count = fn.size();
	for (size_t i = 1; i < 2; i++) //try for an image first, if works, then try for all images in folder
	{
		pic = imread(fn[i], CV_LOAD_IMAGE_COLOR);
		cout << fn[i] << endl;

		cvtColor(pic, gray, CV_BGR2GRAY);
		//Canny(gray, gray, 50, 150, 3);

		threshold(gray, bw, 128.0, 255.0, THRESH_BINARY);

		std::vector<Vec3d> myVec;
		for (int c = 0; c < bw.cols; c++)
		{
			for (int r = 0; r < bw.rows; r++)
			{
				if (bw.at<uchar>(r, c) > 0) // white pixels
				{
					double z = 3.1209;
					//myVec.push_back(Point(r, c));
					myVec.push_back(Vec3d(c, r, z)); //add them to vector3d

					//cout << " : " << myVec.at<Vec3d>myVec.r << " , " << myVec.at<Vec3d>myVec.c << " , " << z << endl;
				}
			}
		}
		
		//std::copy(myVec.begin(), myVec.end(), std::ostream_iterator<Vec3d>(std::cout << " " << std::endl));
		//std::cout << "size: " << myVec.size() << '\n';
		//std::cout <<  myVec.at(myVec.size() - 1);
		//std::cout << ' ' << myVec.at(100) << '\n';


		//failed attempt
		/*std::vector<Vec3d> myVec;
		for (int l = 0; l<3; l++)
		{
			for (int m = 0; m<3; m++)
			{
				for (int n = 0; n < 3; n++)
				{
					cout << myVec[l][m][n] << "\t";
				}
			}
			cout << endl;
		}*/
		//myVec[c][r][z] = [492, 477, 3.1209];
		//double getX();
		//cout << myVec.getX(1846) << '\n';
		//sort(myVec.begin(), myVec.end(), sortcol);
		//auto min = std::min_element(myVec.begin(), myVec.end(), sortcol);
		//auto max = std::max_element(myVec.begin(), myVec.end(), sortcol);
		//std::cout << min << '\n';
		//std::cout << max << '\n';

		//cout << "Before:" << endl;
		//Show(myVec);
		//cout << endl;

		//cout << "After:" << endl;
		sort(myVec.begin(), myVec.end(), PointComparer);
		std::copy(myVec.begin(), myVec.end(), std::ostream_iterator<Vec3d>(std::cout << " " << std::endl));
		//Show(myVec);

		//cout << endl;
		cout << "AveragePoint of points[0] and points[" << myVec.size() - 1 << "]:" << endl;
		ShowPoint(AveragePoint(myVec[0], myVec[myVec.size() - 1]));

		//cout << a[0] << endl;
		//cout << p[0] << endl;
	}

	system("PAUSE");
	//return 0;
}
Last edited on
icy1 (596)
Hi Glacous,

1. I only did the typedef because I didn't want to include opencv and to make the example runnable online. typedef is used for aliasing. In my example, typedef array<double,3> Vec3d; , from then on anywhere I used Vec3d can and will be replaced by array<double,3> at compile time. It's used when there are especially long namespaces just to shorten the code and hopefully make it more readable. In the OpenCV documentation, as I had linked somewhere (your last forum post?), their Vec3d looks very similar to that. Use their original structure; you don't need to typedef. It's like a vector in the mathematical sense; I doubt it has, for example, a push_back() method defined.

2. AveragePoint just averages any two points you give it. Doesn't iterate over anything. I just demo'd its usage on the first and last points of the sorted collection.
PointComparer -- so the classic comparator functions usually just return a<b and are done. When sorting based on multiple criteria, you isolate each criterion. In this case, I preferred to sort by point[0] first, then by point[1], then point[2]. If it gets by the first two if statements, that means a[0]==b[0] and so we examine the next index. So indirectly the equals cases are accounted for. The last line would probably work with a[2]<b[2] as well; it just might perform a swap if all coordinates are equal.
Show() function -- for(auto& : v) and for(auto : v) is the difference between references and value copies during the iteration, as each element in turn is assigned to auto. Prefer references; can also qualify with const.

3. I think the whole thing together (that is, one Vec3d) represents a point in an image.
I could be wrong; maybe it's the colors that the pixel consists of, and it's r,g,b instead of x,y,z. Again, you should prob read their docs.

4. You can have as many std::vector s as you want. For each image, you're writing to "pic", then to "gray", then to "bw", and creating a new vector to store points that meet some criteria. You could make multiple vectors here to store different things as you iterate through rows/cols of your cv::Mat, sure.

5. If you want the average X of all the points in your std::vector<Vec3d> , just use AverageCoordinate function. To get X you'd need the index in your vector first... myVec[i][0].

Good luck in your project. You may need to look more carefully to see what it is exactly you're working with; maybe they're not coordinates after all.
Glaucous (24)
Thank you icy1 for the useful input.

I was caught up with the old project, finally back to this.
I understand that if {0.0, 0.4, 0.7} is the first entry,
then myVec[i][0] get 0.0, myVec[i][0] = 0.4, and so forth.

But here I have one last concern with this multidimensional array thingy.

1. I want to get z before I proceed with other steps, but i am stuck here, hard.
z = x.midpoint - respective x

in the code, i went like below to get the value of x.
I am dazed that it is not working. the line 'int g = myVec[i][t];'
is where some exception thrown comes in. I checked it online, but I couldn't see how it helps. *sweating
Then I tried myVec[c][0] or myVec[c][1], with hope that it gives the value of first x and second x, but no luck.

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		int t = 0;
		
		std::vector<Vec3d> myVec;
		for (int c = 0; c < bw.cols; c++)
		{
			for (int r = 0; r < bw.rows; r++)
			{
				if (bw.at<uchar>(r, c) > 0) // white pixels
				{
					

					t += 3;
					int g = myVec[i][t]; //fail attempt: using avg[0]-x

					myVec.push_back(Vec3d(c, r, g));
				}
			}
		}



2. To get accurate results, I realised that I have to find the largest x and smallest x with same y.
So I am thinking to get lowest y or y = someValue, then with the same y, take (largestX+lowestX)/2.
Is it possible to do that?
I tried to google, usually they are using max element to get the largest without concerning about the value of y.
I could get int smallY = myVec[i][1], but what about get all x from same y?

3. https://www.geeksforgeeks.org/multidimensional-arrays-c-cpp/
It stated that x[i][j][k] to get the value in the location. then , I am a bit curious how did in this case myVec[i][0] can already get first element in first row?
How is it different ?
If you think that I might have overlooked some important fact, I dont mind reading to figure out. I am just stuck.

Thank you and have a great day .
And yes, I'll see what I am getting, if i dont try i wouldnt know if they are coordinates or something else for me. ;)
icy1 (596)
1. Looks like you didn't add it to myVec yet but are already trying to access it? Spend time conditionally adding to myVec and in a completely separate loop you should iterate over myVec and do stuff with it.

2. So make a comparator to sort based on Y, then X, then Z. After sorting, you'll have chunks of equal Y that start with minX and end with maxX.

Edit: On the topic of '<=' in comparators -- after I did some more research, you should just use '<' throughout since that conforms to 'strict weak ordering'. I've corrected my comparators to now have '<' everywhere.

3. Idk, confirm the contents of your bw or myVec or w/e are what you expect them to be.
Last edited on
Glaucous (24)
Thanks icy1 !

1. ouch ! what a silly mistake i made ! Thank you for noticing.
I have got all the x values now. I have one more question . Sorry and thank you..

2. Below is the code I wrote for
- storing all x and y values of 1st image in 2d vector when y is smallest in myVector
- get the average x point, (big x-small x)/2 from 1st column in the 2d vector, newVector
- I can't figure this out yet. Do you have slight idea on how to decide the y is smallest? only when it has at least 5 entries of x with same y values.
- eg. y = 0, has this order of x and y values : [1, 0] [2, 0] [3, 0].
- y = 1 has [1, 1] [5, 1] [33, 1] [33, 1] [49, 1]
- so deciding y = 1 is the small y.

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//myVec[row][column]
int small = myVec[0][1];
		
std::vector<Vec2d> newVec;
if (i == 0) { //in 1st image ONLY
cout << fn[i] << endl;		
for (int t = 1; t < myVec.size(); t++)
	if (myVec[t][1] < small)
		{
			small = myVec[t][1];
			newVec.push_back(Vec2d(t, 1)); //so newVec only store all x and y values when y is lowest 
		}
}

double avg = AveragePoint(newVec[0], newVec[newVec.size() - 1]) / 2.0; //this line
cout << avg << endl; //get only single avg 'x' value from 1st column

//I am having this error in code, on 'this line' no suitable conversion function from "cv::Vec<double, 3>" to "double" exists
//even after I changed the function in AveragePoint to
//	avg = (a[0] + b[0]) / 2.0;
//	return avg;



Thank you for being so helpful.
Last edited on
Glaucous (24)
I made some correction to the code,

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//myVec[row][column]
double small = myVec[0][1];
		
std::vector<Vec2d> newVec;
if (i == 0) { //in 1st image ONLY		
for (int t = 1; t < myVec.size() -1; t++)
	if (myVec[t][1] < small)
		{
			small = myVec[t][1];
			newVec.push_back(Vec2d(myVec[t][0], myVec[t][1])); //so newVec only store all x and y values when y is lowest 
		}
}

double avg = AveragePoint(newVec[0], newVec[newVec.size() - 1]) / 2.0; //this line
cout << avg << endl; //get only single avg 'x' value from 1st column

//I am having this error in code, on 'this line' no suitable conversion function from "cv::Vec<double, 3>" to "double" exists
//even after I changed the function in AveragePoint to
//	avg = (a[0] + b[0]) / 2.0;
//	return avg;


Still when I run this line, I get nothing but an empty vector
std::copy(newVec.begin(), newVec.end(), std::ostream_iterator<Vec2d>(std::cout << " " << std::endl));
Last edited on
Glaucous (24)
Can anybody help?

I can't figure this out yet. Does anyone have slight idea on how to decide the y is smallest only when it has at least 5 entries of x with same y values?

- eg. y = 0, has this order of x and y values : [1, 0] [2, 0] [3, 0].
- y = 1 has [1, 1] [5, 1] [33, 1] [33, 1] [49, 1]
- so deciding y = 1 is the small y.

The code that I now have only finds the smallest y values, and save those xyz in new vector. Also able get the average of biggest x + smallest x divide by 2. 

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//myVec[row][column]
double small = myVec[0][1];

		std::vector<Vec3d> newVec;
		if (i == 0) //in 1st image ONLY
		{
			for (int t = 1; t < myVec.size(); t++)
			{
				if (myVec[t][1] < small)
				{
					small = myVec[t][1];
				}
			}

			for (int s = 0; s < myVec.size() - 1; s++)
			{
				if (myVec[s][1] == small)
				{
					newVec.push_back(Vec3d(myVec[s][0], myVec[s][1], myVec[s][2]));
					//so newVec only store all x and y values when y is lowest 
				}

			}

			a = newVec[0][0];
			b = newVec[newVec.size() - 1][0];

		}

		double avg = (a + b) / 2; //get only single avg 'x' value from 1st column
		//cout << avg << endl;



Thank you very much.
Last edited on
icy1 (596)
Didn't just want to make a comparator to sort based on Y, then X, then Z and afterwards examine those chunks?

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#include <iostream>
#include <array>
#include <vector>
#include <algorithm>

using namespace std;

// Similar to Vec3d
typedef array<double,3> Vec3d;

// From a collection of points, compare based on Y, then X, then Z
bool YPointComparer(const Vec3d& a, const Vec3d& b)
{
    if (a[1] < b[1]) return true;
    if (a[1] > b[1]) return false;
    
    if (a[0] < b[0]) return true;
    if (a[0] > b[0]) return false;
    
    return a[2] < b[2];
}

void ShowPoint(const Vec3d& p)
{
    cout << "[" << p[0] << ", " << p[1] << ", " << p[2] << "]\n";
}

void Show(const vector<Vec3d>& v)
{
    for(auto& p : v)
        ShowPoint(p);
}

// From set of points sorted by Y, find 
//   min Y with at least <required> points with that Y, >= 2.
// If nothing satisfies, returns -1.0
double MinY(const vector<Vec3d>& a, int required=2)
{
    double best_y;
    int chunk_size;
    for (int i=0; ; )
    {
        best_y = a[i][1];
        chunk_size = 1;
        if (++i == a.size())
            return -1;
            
        while (a[i][1]==best_y)
        {
            if (++chunk_size == required)
                return best_y;
            
            if (++i == a.size())
                return -1;
        }
    }
    return best_y;
}


int main() 
{
    vector<Vec3d> points = 
    {
        {33, 1, 196},
        {3, 0, 224},
        {33, 1, 117},
        {4, 2, 114},
        {2, 0, 116},
        {5, 3, 255},
        {1, 0, 44},
        {1, 1, 190},
        {5, 1, 21},
        {16, 3, 29},
        {49, 1, 69},
        {4, 4, 4},
        {4, 3, 3}
    };
    
    cout << "Before:" << endl;
    Show(points);
    cout << endl;
    
    cout << "Sort by Y, then X, then Z:" << endl;
    sort(points.begin(), points.end(), YPointComparer);
    Show(points);

    cout << endl;
    int req = 2;
    cout << "Min Y with at least "<<req<<" of the same" << endl;
    cout << MinY(points, req) << endl;
    req = 5;
    cout << "Min Y with at least "<<req<<" of the same" << endl;
    cout << MinY(points, req) << endl;
    req = 6;
    cout << "Min Y with at least "<<req<<" of the same" << endl;
    cout << MinY(points, req) << endl;

    return 0;
}


https://repl.it/repls/SoulfulShinyCad 

Before:
[33, 1, 196]
[3, 0, 224]
[33, 1, 117]
[4, 2, 114]
[2, 0, 116]
[5, 3, 255]
[1, 0, 44]
[1, 1, 190]
[5, 1, 21]
[16, 3, 29]
[49, 1, 69]
[4, 4, 4]
[4, 3, 3]

Sort by Y, then X, then Z:
[1, 0, 44]
[2, 0, 116]
[3, 0, 224]
[1, 1, 190]
[5, 1, 21]
[33, 1, 117]
[33, 1, 196]
[49, 1, 69]
[4, 2, 114]
[4, 3, 3]
[5, 3, 255]
[16, 3, 29]
[4, 4, 4]

Min Y with at least 2 of the same
0
Min Y with at least 5 of the same
1
Min Y with at least 6 of the same
-1
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