Trouble writing to 4D vector in C++ (no viable overloaded '=') - c++

Question

The issue I am facing is that via the openCV library I am reading in a series of images as their own "Mat" format: an image matrix.
Basically I need to write any pixel value that's > 0 as "true" to a 4D vector and any that == 0 as "false".
Why 4 dimensions?
vector<vector<vector<bool>>>pointVector;
The 3 vector levels refer to X,Y,Z axes. Bool is just the true/false. The images are Y by Z and are stacked in 3D along axis X.
Basically we have a series of images representing points that are stacked in 3D.
(Poor explanation? Probably)
Anyway, the issue comes in my function to read the points in a single photo then write them out to the 4D vector.
Note: xVal is a global storing the ID number of the photo addressed. It's used for the X dimension (layers of images).
Int lineTo3DVector (Mat image)
{
// Takes in matrix and converts to 4D vector.
// This will be exported and all vectors added together into a point cloud
vector<vector<vector<bool>>>pointVector;
for (int x=0; x<image.rows; x++)
{
for (int y = 0; y<image.cols; y++)
{
if((image.at<int>(x,y)) > 0)
{
pointVector[xVal*image.cols*image.rows + x*image.cols + y] = true;
}
}
}
}
I haven't finished writing all of the function because the if statement intended to write pointVector at address xVal, x, y with bool 'true' throws up an error saying:
No viable overloaded '='
Any idea what's going wrong? I've scoured the web and given myself a headache trying to dig up info (yeah, noob in the deep-end again) so any suggestions would be appreciated.

Answer 1

You're accessing only the first vector (the outer one), without actually accessing any of the vectors inside.
The syntax would be pointVector[x][y][z] = true, where x, y and z are the values you want to use to access the three nested vectors.
What you want is:
pointVector[xVal][x][y] = true
What you were using is a way to access a 3D array that is laid out in memory as a 1D array, but it's not what you want in your case.
Make sure you don't go out of bounds
Make sure the elements you are accessing actually exist! If the code you have shown is the actual code, pointVector will have no elements when you try to use it.
To fix that, you have to resize all the vectors (outer and inner). This can get cumbersome, and you may want to go with the 1D approach, i.e. allocate a large, one-dimensional bool array and access it using the method you were using (largeArray[xVal*image.cols*image.rows + x*image.cols + y]).
1D approach
In the following code numberOfValues is the maximum number of elements you will access.
int lineTo3DVector (Mat image)
{
// Takes in matrix and converts to 4D vector.
// This will be exported and all vectors added together into a point cloud
std::vector<bool> pointVector;
pointVector.resize(numberOfValues);
for (int x=0; x < image.rows; x++)
{
for (int y = 0; y < image.cols; y++)
{
if(image.at<int>(x,y) > 0)
{
pointVector[xVal*image.cols*image.rows + x*image.cols + y] = true;
}
}
}
// Return whatever.
}