# HALOWERK Eastern Land – Croatia Mean Surface Slope

> HALOWERK Eastern Land – Croatia Mean Surface Slope is a paid API for AI agents from ostland.halowerk.com, paid per call via x402, $0.003/call, status unknown (last checked 2026-09-15).

Returns the mean first-order surface gradient (slope) across the analysis grid for a given coordinate within Croatia's boundary.

## Facts

- Endpoint: POST https://ostland.halowerk.com/v1/hr-mean-slope
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/halowerk-eastern-land-croatia-mean-surface-slope-3b6ac232
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_qiKGQ-Zl9TYtyPXg6py2U

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability halowerk-eastern-land-croatia-mean-surface-slope-3b6ac232 -d '<json body>'
```

Example prompt: What's the mean surface slope at latitude 45.5, longitude 16.2 in Croatia? I need the average terrain gradient for that location.

## When to prefer this

Choose this endpoint when you need the mean (average) surface slope metric specifically for a coordinate within Croatia, as opposed to maximum slope, elevation range, or other terrain derivatives. It is distinct from sibling endpoints offering max gradient, elevation standard deviation, or ruggedness index. Ideal for agricultural, environmental, or construction workflows requiring a smooth, averaged gradient signal rather than extreme values.

## Known failure modes

- Coordinate outside Croatia's Natural Earth boundary — request rejected before payment with a boundary validation error
- Latitude or longitude outside the published European coverage range (lat 34–72.5, lon -31.5–40.5) — schema validation error
- Malformed or missing latitude/longitude fields — request rejected with input validation error
- Network timeout or service unavailability — HTTP 5xx response

## How this service works

Mean first-order surface gradient across the analysis grid. The coordinate is validated against the Natural Earth boundary for Croatia; results outside it are rejected before payment.

## Output

A numeric value representing the mean first-order surface gradient (slope) across the analysis grid centered on the requested coordinate within Croatia. Coordinates outside the Natural Earth boundary for Croatia are rejected before any charge is applied.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "latitude": {
   "type": "number",
   "maximum": 72.5,
   "minimum": 34,
   "description": "WGS84 latitude inside the published European coverage."
  },
  "longitude": {
   "type": "number",
   "maximum": 40.5,
   "minimum": -31.5,
   "description": "WGS84 longitude inside the published European coverage."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/halowerk-eastern-land-croatia-mean-surface-slope-3b6ac232/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from ostland.halowerk.com](https://www.zero.xyz/host/ostland.halowerk.com/llms.txt)