Cross Section at a Point

Extract a cross-sectional elevation profile at a single point along an NHDPlusV2 flowline.

Overview

The cross section at a point process (nldi-xsatpoint) extracts a cross-sectional elevation profile perpendicular to an NHDPlusV2 flowline at a single user-specified location. The user provides a coordinate, a transect width in meters, and the number of elevation sample points.

How It Works

  1. The user supplies a coordinate (lat/lon), a width in meters defining how wide the cross section should be, and numpts specifying how many elevation sample points to generate.
  2. The process identifies the nearest NHDPlusV2 flowline and determines the perpendicular orientation at the intersection point.
  3. The process samples elevation data at evenly spaced points along the perpendicular transect.
  4. The process returns a JSON response containing the elevation profile.

Potential applications include:

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

Example Request

Extract a 1000-meter-wide cross section with 101 sample points at a location in Kansas:

POST https://api.water.usgs.gov/nldi/pygeoapi/processes/nldi-xsatpoint/execution?f=json
Content-Type: application/json

{
  "inputs": {
    "lat": 39.064867,
    "lon": -96.168776,
    "width": 1000.0,
    "numpts": 101
  }
}

width is the total transect width in meters, centered on the flowline. numpts controls the resolution of the elevation profile — more points means finer detail but a larger response.

Explore the Full Parameter Schema

The pygeoapi process description provides the complete parameter schema: /processes/nldi-xsatpoint?f=json