Description
Convert grain diameter in millimetres to the phi scale, or convert phi back to diameter.
Geomorphic measurements distinguish signed coordinates, grain-size scales, profile derivatives and transported-mass or cross-section bases. A supplied datum adjustment or threshold does not detect a landform or establish a process. Plan distance, profile second derivative and slope-normalized curvature are different quantities.
Convert grain diameter in millimetres to the phi scale, or convert phi back to diameter.
When to use this tool
Use Sediment Grain Phi Diameter Crosswalk when checking the stated local landform, sediment, profile or coordinate convention.
How to use the tool and how it works
- Enter value, direction. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read converted. Use the output convention below.
Choose millimeters-to-phi or phi-to-millimeters. Positive diameter converts as -log2(diameter_mm); phi converts as 2^(-phi) millimetres, rejecting nonpositive underflowed or nonfinite results.1
The phi scale uses minus the base-two logarithm of grain diameter expressed in millimetres. A larger phi therefore represents a smaller diameter.2
| Input field | Meaning and units | Accepted input |
|---|---|---|
| value | Millimetre diameter>0 in millimeters-to-phi mode, or signed dimensionless phi in reverse mode. | Required. Finite number. |
| direction | Direction | Required. Text; one of "millimeters-to-phi", "phi-to-millimeters"; maximum UTF-16 length 8192. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| converted | Converted | Required. Finite number. |
{
"input": {
"value": 0.25,
"direction": "millimeters-to-phi"
},
"output": {
"converted": 2
}
}Limitations and assumptions
- The one-millimetre reference is part of the phi convention; no grain sample, size distribution or sediment class is inferred.
- 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 calibrated surveys, mapped geometry and suitable complete sediment/terrain models for trends, process interpretation, uncertainty or hazard assessment.
References
-
Calculation and input contract: geomorphology/sediment-grain-phi-diameter-crosswalk — tool.io
-
Environmental Effects of Sand Mining in the Lower Bay of New York Harbor, Phase 1: grain-size conversion chart — New York Sea Grant Institute; NOAA repository
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