Evidence Scale Perspective Length Factor Tool

Description

Return ruler-scaled length, then multiply it by objectDepth/rulerDepth.

Forensic measurement calculations require a known calibration, geometric model and uncertainty convention. A converted length, ratio or residual describes the supplied measurements; it does not establish common origin, identity or evidentiary strength.

Return ruler-scaled length, then multiply it by objectDepth/rulerDepth.

When to use this tool

Use Evidence Scale Perspective Length Factor when you need an explicit image or physical-measurement term.

How to use the tool and how it works

Enter objectPixels, rulerPixels, rulerLength, objectDepth, rulerDepth. Use the units and conventions below.
Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
Read uncorrectedLength, correctedLength. Use the output convention below.

Require nonnegative objectPixels and positive ruler pixels/length and both camera depths. Return ruler-scaled length, then multiply it by objectDepth/rulerDepth.^[1]

Input field	Meaning and units	Accepted input
objectPixels	Object Pixels	Required. Finite number; minimum 0.
rulerPixels	Ruler Pixels	Required. Finite number; strictly above 0.
rulerLength	Ruler Length	Required. Finite number; strictly above 0.
objectDepth	Object Depth	Required. Finite number; strictly above 0.
rulerDepth	Ruler Depth	Required. Finite number; strictly above 0.

Output field	Interpretation	Returned shape
uncorrectedLength	Uncorrected Length	Required. Finite number.
correctedLength	Corrected Length	Required. Finite number.

json

{
  "input": {
    "objectPixels": 100,
    "rulerPixels": 50,
    "rulerLength": 10,
    "objectDepth": 2,
    "rulerDepth": 1
  },
  "output": {
    "uncorrectedLength": 20,
    "correctedLength": 40
  }
}

Limitations and assumptions

Depths share units and follow the same ideal pinhole-camera convention. Perspective geometry is supplied rather than recovered, and no source identification follows.
Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.

Alternative or Complementary methods

Use the validated measurement method and original evidence for interpretation. Include calibration, geometry, uncertainty and the full evidentiary context rather than turning a numerical match into an identification.

References

Calculation and input contract: forensic-science/evidence-scale-perspective-length-factor — tool.io

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