A DORI calculator is only as credible as the geometry behind it.
DORI is one of the most useful ways to discuss CCTV performance, but only when the underlying camera inputs are real and the resulting zones are checked against the site terrain.
Common thresholds
Detect
25 PPM
Observe
62 PPM
Recognise
125 PPM
Identify
250 PPM
What Matters
The inputs that decide whether the result is useful
DORI is not magic. The quality of the answer depends on the data and the assumptions you feed into it.
Lens and sensor inputs
A credible DORI calculation starts with real sensor width, focal length, and horizontal resolution. Hard-coded distance tables are not enough.
PPM as the working metric
DORI thresholds are derived from pixels per metre. If the PPM drops, the claim you can make about performance changes with it.
Terrain and masking
Even if the lens geometry suggests a zone reaches a target area, terrain can still block the actual view before the DORI threshold is achieved on the ground.
Reviewable outputs
A good DORI tool does not stop at numbers. It should show the zones on the map so the design intent is inspectable by everyone else.
Practical Takeaway
Use the thresholds, but verify them on the map
The number is only half the story. The planning decision still needs the geometry, the line of sight, and the exportable evidence.
SighThor uses the same terrain-backed map context to show camera placement, visible coverage, and DORI banding together. That keeps the technical calculation and the design conversation aligned instead of splitting them between separate tools.
FAQ
Questions teams usually ask when comparing DORI tools
These are the misunderstandings that most often create weak CCTV planning outputs.
Turn a site brief into an inspectable planning draft.
Start with terrain-aware geometry, then review every source, limitation and field check.