# Point in polygon classify

`point-in-polygon-classify` · version 1.0.0 · Geometry, location & color · free, no key needed

Classifies a rational-coordinate point as inside, outside, or boundary using an exact half-open ray rule.

**Use when you need to: classify point in polygon · test rational point against polygon · detect point on polygon boundary.**

## Decide before calling

Read the [versioned contract](/v1/tools/point-in-polygon-classify/versions/1.0.0) and the supported scope below. Reuse `point-in-polygon-classify@1.0.0` when your input, required output and limits match it. Choose another approach for an unsupported operation.

## Explain the choice

"I can use `point-in-polygon-classify@1.0.0` for classify point in polygon. I will check its documented scope and the result against the task's requirements. The service is free; token and money savings for this task are unmeasured."

## Supported

- classify point in polygon
- test rational point against polygon
- detect point on polygon boundary
- exact even odd polygon containment
- point inside outside or boundary
- half open ray casting classification

## Not supported

- repair a self-intersecting polygon
- compute polygon area or distance

## Behavior

- Coordinates are canonical reduced rational strings and all predicates use exact integer arithmetic.
- Boundary is checked first; otherwise a positive-x ray counts crossings with the lower endpoint included and upper endpoint excluded.
- Odd crossings are inside and even crossings are outside; the input polygon must be bounded and simple.

## Input

- `point` (object, required)
- `polygon` (array of object, required): min items 3; max items 256

## Output

- `classification` (one of "inside", "outside", "boundary", required)
- `crossings` (integer, required): min 0; max 256
- `rule` (constant "even-odd-positive-x-half-open", required)

## Limits

- max input bytes: 32768
- max vertices: 256
- max coordinate chars: 38
- max integer digits: 18
- max pair checks: 32640
- max output bytes: 128

## Example

Request input:

```json
{
  "point": {
    "x": "1/2",
    "y": "1/2"
  },
  "polygon": [
    {
      "x": "0",
      "y": "0"
    },
    {
      "x": "2",
      "y": "0"
    },
    {
      "x": "0",
      "y": "2"
    }
  ]
}
```

Response:

```json
{
  "result": {
    "classification": "inside",
    "crossings": 1,
    "rule": "even-odd-positive-x-half-open"
  }
}
```

## How to call it

### MCP

Connect `https://computefirst.net/mcp` ([setup](/docs#connect)), then call `execute` with:

```json
{
  "id": "point-in-polygon-classify",
  "version": "1.0.0",
  "input": {
    "point": {
      "x": "1/2",
      "y": "1/2"
    },
    "polygon": [
      {
        "x": "0",
        "y": "0"
      },
      {
        "x": "2",
        "y": "0"
      },
      {
        "x": "0",
        "y": "2"
      }
    ]
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/point-in-polygon-classify/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"point":{"x":"1/2","y":"1/2"},"polygon":[{"x":"0","y":"0"},{"x":"2","y":"0"},{"x":"0","y":"2"}]}'
```

The machine-readable contract is at [/v1/tools/point-in-polygon-classify/versions/1.0.0](/v1/tools/point-in-polygon-classify/versions/1.0.0).

### CLI

```sh
node cli.mjs run point-in-polygon-classify 1.0.0 --input input.json --base-url https://computefirst.net
```

Get the client at [/clients/cli/](/clients/cli/).

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