def get_capillary_diameter(line1, line2):
    """
    Defines capillary diameter in pixel length.
    
    line1 = int32 - first point on left edge of capillary
    line2 = int32 - second point on right edge of capillary
    """     
    #express first points on opposite side of capillary as x,z coordinates
    L1x,L1y = line1
    L2x,L2y = line2
    
    #find straight line distance between points
    dist = ((L2x-L1x)**2+(L2y-L1y)**2)**0.5

    #Assumption: rotation of image is very small such that the scaled straight
    #line distance is very close to true diameter of the capillary 
    return dist