Index Contour Every Nth Selector Calculator

Select every Nth contour ordinal aligned to caller origin, including signed below-datum indices; no elevation rounding.

Description

Index Contour Every Nth Selector Calculator: return index contour ordinals.

Index contours emphasize every nth contour relative to an origin. Using ordinals makes the selection independent of elevation units.

This tool returns index contour ordinals. 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 integer ordinals, a positive everyNth and an integer originOrdinal. Keep entries whose ordinal minus origin is divisible by everyNth.^[1]

Input field	Meaning and units	Accepted input
contourOrdinalIndices	Contour ordinal indices.	List of finite numbers
everyNth	Every nth.	Integer; from 1 to 1000000 inclusive
originOrdinal	Origin ordinal.	Integer; from -1000000 to 1000000 inclusive

Output field	Interpretation
result	Object containing the following named result fields.
result.indexContourOrdinals	Index contour ordinals list, in the ordering described in the calculation.

json

{
  "input": {
    "contourOrdinalIndices": [
      0,
      1,
      2,
      3,
      4,
      5
    ],
    "everyNth": 2,
    "originOrdinal": 0
  },
  "output": {
    "result": {
      "indexContourOrdinals": [
        0,
        2,
        4
      ]
    }
  }
}

Limitations and assumptions

The tool preserves input order and does not generate contour geometry or infer contour elevations.
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

Tool behavior and example: Index Contour Every Nth Selector Calculator — tool.io

Similar or alternative tools

contour density per cm checker
Number of contour crossings per map centimetre from a count along a measured map transect.
slope percent contour spacing
Horizontal spacing in metres between contours from vertical interval and grade percentage.