Here's a schematic of Marcus' environment and the approximate path he follows through it. In the meantime, here's a number of movies of Marcus doing his thing. On day I'll get around to explaining the explanations. In the following clips, the overlayed text does not correspond to the exact moment when Marcus asks his human assistant for help. These subtitles were meant to supplement the soundtrack of the original video, which is not captured in these movies.
Some clips are of the laptop screen with processed images and overlayed graphics.
Marcus asks for the yellow block to be picked up. He first finds the yellow block by going to the purple block and then searching the area around the yellow block's expected position. Upon finding the yellow block, he drives up to it and asks for a pickup. The processed images from the preceeding clip. An important point here is that Marcus is not actually searching for just a yellow block.