Photo-based measurement
A top-down photo shows the roof outline but not its height. Pitch has to come from somewhere else: entered by hand, estimated from shadows and shape by software, or measured across several oblique photos (photogrammetry). Single-image methods can look precise while guessing the one number that changes the area most. Outlines can also be shifted by camera lean and hidden by overhangs and trees.
LiDAR-based measurement
Airborne LiDAR sends laser pulses from an aircraft and records where each return lands in 3D. Public programs such as the USGS 3D Elevation Program collect most current U.S. data at Quality Level 2 or better — at least 2 points per square meter with about 10 cm vertical accuracy. On a typical roof that is hundreds to thousands of measured points. Fitting planes to them gives the pitch of each facet from its measured height, not from its appearance.
Limits of each
| Photo | LiDAR | |
|---|---|---|
| Pitch | Entered, inferred, or multi-angle photogrammetry | Measured from point heights |
| Date | Often recent | Survey date — can be several years old |
| Trees | Hide the roof | Partly see through gaps; dense canopy still hides it |
| Small details | Visible if the image is sharp | Can fall between points |
What to check before you trust any remote number
- The date of the imagery or survey — new additions and re-roofs after it are not in the data.
- Where the pitch came from — measured, or typed in or guessed?
- What is excluded — porches, garages, unknown surfaces. A good report says what it left out.
- Edge lengths — ridge, hip, valley, eave and rake drive the accessory order.
Roofari shows the survey and its year on every result and says so when the data are not good enough, instead of inventing a number. Our data sources →
Questions
Is LiDAR more accurate than satellite imagery for roofs?
For pitch, LiDAR measures height directly, while a single satellite image has to infer it. For outlines both can be good. The survey date and tree cover matter for both.
How old is the LiDAR data?
It depends on the area; public surveys are typically repeated every several years. Roofari shows the survey and year on every result.