Topographic Position Index TPI Difference Calculator
Signed center elevation minus unweighted actual neighborhood mean; no standardized landform class.
Description
Topographic Position Index TPI Difference Calculator: return tpi meters.
Topographic Position Index compares a cell's elevation with its neighborhood mean. The selected neighborhood controls the scale of the comparison.
This tool returns tpi meters. Use the stated units and model convention when interpreting these fields.
When to use this tool
Use this tool when the supplied inputs match the specific operation described above and you need a repeatable result under its stated convention.
- Check the supported input and output contract against an existing calculation or observation.
- Use the complete example to confirm units, selector spelling and result interpretation.
How to use the tool and how it works
- Enter every field in the input table using the stated units and the exact supported selector spelling where applicable.
- Run the tool. Correct input errors before interpreting an output.
- Read the result fields below; use accompanying flags and the stated sign, boundary or model convention when interpreting a number.
Require at least one neighbor, subtract the mean neighbor elevation from centerElevationM and return the difference in meters.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| centerElevationM | Center elevation m. Meters. | Finite number |
| neighborElevationsM | Neighbor elevations m. Meters. | List of finite numbers |
| Output field | Interpretation |
|---|---|
| result | Object containing the following named result fields. |
| result.tpiMeters | Tpi meters; use the stated units and sign convention. |
{
"input": {
"centerElevationM": 10,
"neighborElevationsM": [
2,
4
]
},
"output": {
"result": {
"tpiMeters": 7
}
}
}Limitations and assumptions
- The tool does not select a neighborhood radius or classify a complete landform.
- Every declared field is required and unexpected fields are rejected. Numeric inputs must be finite; input errors are distinct from a valid false result or an explicitly qualified output.
- Extremely large inputs and nonfinite or excessively large outputs are rejected. List positions reported by the tool use zero-based indices unless stated otherwise.
Alternative or Complementary methods
Check the underlying observations, units and conventions independently before using the result in a larger workflow. The tools listed below address nearby tasks; compare their inputs and scope before substituting one for this operation.
References
Similar or alternative tools
- Index Contour Every Nth Selector Calculator
Select every Nth contour ordinal aligned to caller origin, including signed below-datum indices; no elevation rounding.
- Terrain Ruggedness Index Cell Calculator
Riley TRI sqrt(sum squared center-neighbor elevation differences), exactly eight caller observed neighbors.