In an example embodiment, a first set of estimated locations for calibration points in a roof is identified in a first satellite image, the first satellite image having a first zoom level and a first angle relative to ground. Then a second set of estimate locations for the calibration points is identified in a second satellite image, the second satellite image having a second zoom level and a second angle relative to ground. Actual locations for the calibration points are derived using the first and second sets of estimated locations, the first and second zoom levels, and the first and second angles. Then dimension information is calculated for the roof based on the derived actual locations for the calibration points.