Keystone Correction Angle Calculator
Declared planar trapezoid SIDE wall angle from signed(top width−bottom width)/(2height), not infer projector tilt/lens geometry or actual correctivehomography.
Description
A projected trapezoid's side angle can be calculated from its measured top and bottom widths and height.
A projected trapezoid's side angle can be calculated from its measured top and bottom widths and height.1
This tool returns that signed geometric angle without inferring projector tilt or constructing a corrective homography.
When to use Keystone Correction Angle Calculator
Use this tool to obtain that signed geometric angle without inferring projector tilt or constructing a corrective homography.
How to use Keystone Correction Angle Calculator and how it works
- Prepare actualProjectedTopWidth, actualProjectedBottomWidth, actualProjectedHeight, with the units, conventions and assumptions below.
- Enter the required fields and run Keystone Correction Angle Calculator.
- Read result.value using the output definitions below.
- Correct any rejected inputs and rerun; interpret the result within the stated model and its assumptions.
| Input field | Meaning | Value type | Requirement |
|---|---|---|---|
| actualProjectedTopWidth | Actual Projected Top Width. Use the units and matching context stated in the calculation below. | number | Required; strictly positive; finite; other constraints below |
| actualProjectedBottomWidth | Actual Projected Bottom Width. Use the units and matching context stated in the calculation below. | number | Required; strictly positive; finite; other constraints below |
| actualProjectedHeight | Actual Projected Height. Use the units and matching context stated in the calculation below. | number | Required; strictly positive; finite; other constraints below |
Supply positive top width, bottom width and image height in one length or pixel unit. Calculate atan((top-bottom)/(2*height)) in degrees and retain its sign. This is the implemented symmetric trapezoid geometry, not a recovered projector tilt or a complete image-warp transform.
angleDegrees=atan((topWidth-bottomWidth)/(2*height))*180/pi Apply the input ordering, units and branch conditions stated above.
| Output field | Meaning | Value type |
|---|---|---|
| result | Object containing the calculated or selected fields below. | object |
| result.value | Signed geometric angle in degrees. | number |
{
"input": {
"actualProjectedTopWidth": 5,
"actualProjectedBottomWidth": 1,
"actualProjectedHeight": 2
},
"output": {
"result": {
"value": 45
}
}
}Limitations and assumptions
The calculation uses the supplied observations and model inputs. It does not collect measurements, select a reference population or coefficient, or establish that the model applies to the actual case. The stated branch conditions and output units remain part of the result.
All fields require explicit values. Unexpected fields, wrong types, nonfinite numbers and sparse arrays are rejected. Alignment, bounds and supported-token rules are explained above; extremely large inputs or nonfinite results can also fail. Input errors differ from successful false comparisons, unavailable-domain flags and empty match lists.
Alternative or Complementary methods
Use Optical Magnification Calculator for a complementary operation: Thin-lens transverse magnification has a signed distance-ratio convention.
Use Lens Maker Equation Calculator for a complementary operation: The thin-lens maker relation depends on relative refractive index and signed surface radii.
References
-
Keystone Correction Angle Calculator — tool.io
Similar or alternative tools
- Optical Magnification Calculator
Thin-lens transverse magnification has a signed distance-ratio convention.
- Lens Maker Equation Calculator
The thin-lens maker relation depends on relative refractive index and signed surface radii.