I have read in a jpeg file of a floor map. Now I want to draw a circle on it of time-dependent radius, so that it appears to be growing with time. I used the function viscircles. At a later time I want to go to a different position within the image and start drawing a new circle. But viscircles draws a filled circle that is persistent. How can I plot new circles and make the earlier circle go away. I could use cla every time I want a new circle, but that would require me to display the background image again. That would add processing time.