Preliminary planning of the exploration and fundraising took more than six years. Before the start of excavations, beginning in the early months of 2004, Dr. Victor Manuel Velasco Herrera determined with the help of ground-penetrating radar and a team of some 20 archaeologists and workers the approximate length of the tunnel and the presence of internal chambers. They scanned the earth under the Ciudadela, returning every afternoon to upload the results to Gómez's computers. By 2005, the digital map was complete. The archaeologists explored the tunnel with a remote-controlled robot called Tlaloc II-TC, equipped with an infrared camera and a laser scanner that generates 3D visualization to perform three dimensional register of the spaces beneath the temple. A small opening in the tunnel wall was made and the scanner captured the first images, 37 meters into the passage.