<qa>  What is the primary aim of this trial?The primary aim of this trial is to demonstrate non-inferiority of lung function response to 5 ug 2 actuations of 2.5 ug of Ba679BR Respimat delivered by the Respimat inhaler once daily compared to tiotropium 18 ug inhaled as powder capsule from the HandiHaler once daily at the end of 4-week treatment periods in patients with COPD. The hypothesis test of non-inferiority will be performed at alpha 0.025 one-sided. 