modified markup to add an overlay canvas. Viewer now checks hover x and y and doesn't lookup up the value in the data array unless they are less than the length of the array
overlay now marks where you click but does not erase previous marks
still can't clear the overlay canvas properly
Merge branch 'overlay'
added jsfiddle link to clear canvas function that doesn't work properly
did a 340 mesh data run at acc=0.31 and improved viewer slightly