Cross Section at Point

Generate a cross section at a single location along a flowline using NLDI pygeoapi services.

Overview

The NLDI pygeoapi service provides a cross section at a point process, which
generates a cross-sectional profile of a flowline at a single user-specified
location. This functionality is part of the Python-based geoprocessing tools
(nldi-flowtools and nldi-xstool) surfaced through the pygeoapi OGC API.

These cross‑section capabilities complement other elevation-driven NLDI tools
such as raindrop trace and split catchment.

How It Works

To create a cross section at a point:

  1. The user supplies a coordinate representing a location along (or near)
    a flowline.
  2. If needed, a hydrolocation step is used internally to derive the correct
    linear-referenced location on the flowline.
  3. The process samples elevation or hydraulic geometry data across the
    flowline perpendicular to the river path.
  4. A line geometry representing the cross section is returned.

This operation supports analyses such as:

  • Bankfull elevation estimation
  • Channel morphology assessment
  • Hydraulic modeling preparation

Inputs and Outputs

Although the source blog post does not provide explicit I/O schemas,
the following high-level description is supported:

Inputs may include:

  • A coordinate (typically WKT POINT(lon lat))
  • Optional parameters related to snapping or projection

Outputs typically include:

  • A line geometry representing the cross section
  • Metadata related to the sampled path

Notes & TODOs

  • TODO: Define required parameters (coordinate format, snapping behavior, CRS).
  • TODO: Specify the expected output schema (geometry type, attribute fields).
  • TODO: Add a Python example once the final process endpoint is available.