there are two type of depth images which is generated from depth camera.The below is the reference for images
Do rtab has option to select between this two types of depth image.For your understanding the first image where the nearest object is plotedd with white and far is plotted with black and in second image the near is pltted with lack and far is plotted with white.If there is an option in Rtab map to select inbetween this two type of depth image that will be really helpfull.