Crate terrand 

terrand — Pure-Rust terrain analysis on ndarray.

Provides DEM (Digital Elevation Model) analysis without GDAL or any C dependencies. All operations take ndarray::Array2<f64> as input and return ndarray arrays as output, making them composable with the rest of the Rust scientific computing ecosystem.

Modules

Module	Operations
slope	Slope in degrees, radians, or percent
aspect	Slope direction as compass bearing
curvature	Profile, plan, and general curvature
hillshade	Shaded-relief illumination
roughness	TRI, TPI, and surface roughness
hydrology	Fill, flow direction, accumulation, watershed, basin, stream order
viewshed	Line-of-sight visibility analysis
contour	Marching-squares contour generation

Quick start

use ndarray::Array2;
use terrand::{slope, aspect, hillshade, CellSize};

// A synthetic DEM with a uniform east-facing slope.
let dem = Array2::from_shape_fn((100, 100), |(_, c)| c as f64 * 10.0);
let cell = CellSize::square(30.0).unwrap();

let s = slope(&dem, cell);
let a = aspect(&dem, cell);
let hs = hillshade(&dem, cell, 315.0, 45.0);

Parallelism

Enable the parallel feature to use Rayon for multi-threaded computation on all per-cell operations:

[dependencies]
terrand = { package = "terrand-rs", version = "0.1", features = ["parallel"] }

NaN and nodata handling

NaN handling is operation-specific. Surface-analysis kernels generally propagate NaN through their 3x3 arithmetic on normal-size grids, but their small-grid fallbacks return documented flat values. Hydrology treats NaN as nodata for elevation rasters: fill leaves NaN cells unchanged, while flow_direction encodes NaN cells as direction 0. Contour generation treats NaN cells as holes and skips quads containing them.

Algorithms

Slope, aspect, and hillshade use the Horn (1981) 3x3 weighted gradient kernel with GDAL-compatible linear extrapolation at grid edges. Curvature uses Horn first-order gradients with the same edge extrapolation, plus finite-difference second derivatives clamped at grid edges.

Re-exports

pub use aspect::aspect;

pub use aspect::ASPECT_FLAT;

pub use cell_size::CellSize;

pub use curvature::general_curvature;

pub use curvature::plan_curvature;

pub use curvature::profile_curvature;

pub use error::Error;

pub use error::Result;

pub use hillshade::hillshade;

pub use hydrology::basin;

pub use hydrology::fill;

pub use hydrology::flow_accumulation;

pub use hydrology::flow_direction;

pub use hydrology::snap_pour_point;

pub use hydrology::stream_order_strahler;

pub use hydrology::watershed;

pub use roughness::roughness;

pub use roughness::tpi;

pub use roughness::tri;

pub use slope::slope;

pub use slope::slope_percent;

pub use slope::slope_radians;

pub use viewshed::viewshed;

pub use viewshed::ViewshedConfig;

pub use viewshed::EARTH_RADIUS_M;

Modules

aspect

Aspect (slope direction) computation from a Digital Elevation Model.

cell_size

Cell-size metadata for regular DEM grids.

contour

Contour line generation using the marching squares algorithm.

curvature

Surface curvature computation from a Digital Elevation Model.

error

Error types returned by fallible terrand operations.

hillshade

Hillshade illumination from a Digital Elevation Model.

hydrology

Hydrological analysis on Digital Elevation Models.

roughness

Terrain roughness indices computed from a 3x3 neighborhood.

slope

Slope computation from a Digital Elevation Model using the Horn algorithm.

viewshed

Viewshed analysis: determine which cells are visible from an observer point.