What's the mean of this code?

[GY56723-debug]

I’m a novice of slam. when i read the this code, I can't realize what it means:

cv::Mat mask;
if (to.type() == CV_32F || to.type() == CV_64F)
mask = (to != to) & (from == from);
else
mask = (to == 0) & (from > 0);

This segment appear in this function:

void CvGridMap::mergeMatrices(const cv::Mat &from, cv::Mat &to, int flag_merge_handling)
{
switch(flag_merge_handling)
{
case REALM_OVERWRITE_ALL:
to = from;
break;
case REALM_OVERWRITE_ZERO:
cv::Mat mask;
if (to.type() == CV_32F || to.type() == CV_64F)
mask = (to != to) & (from == from);
else
mask = (to == 0) & (from > 0);
from.copyTo(to, mask);
break;
}
}

If you responce, i would appreciate it

[laxnpander]

@GY56723-debug Hey, this is not SLAM related. This is just logical operators with one speciality: to != to checks if the matrix "to" is not equal to matrix "to". So it is basically a comparison with itself. The speciality here is: We check for NaNs. As per C++ standard definition comparing a NaN with itself gives false in the logical world.

The whole purpose of this function is to merge two layers (matrices) in a grid map.

• REALM_OVERWRITE_ALL says we simply overwrite the content in grid "to" with the content of grid "from".
• REALM_OVERWRITE_ZERO says we overwrite only zero values in grid "to" with non-zero values of grid "from".

A grid map is the result of the mapping process, one layer could be RGB for example. Another one contains the elevation etc.

[GY56723-debug]

Thanks, I understand now

[laxnpander]

@GY56723-debug You are welcome! Reopen if questions persist.