TopoDroid v. 2. 7 - Cave surveying on Android. You get the most out of your surveying time in the cave. Main functions. Survey data (DistoX recommended). Export formats: therion, compass, visualtopo, walls, survex, csurvey, pockettopo, dxf, csv, kml, track-file. Sketch drafting. Export formats: therion, csurvey, dxf, svg, png. Calibration of DistoX. Advanced DistoX functions.