esri-ascii-grid-rs

Rust library to read ESRI Ascii grid .asc files

Example ASCII Grid:

ncols         4
nrows         6
xllcorner     0.0
yllcorner     0.0
cellsize      50.0
NODATA_value  -9999
-9999 -9999 5 2
-9999 20 100 36
3 8 35 10
32 42 50 6
88 75 27 9
13 5 1 -9999

This library uses buffers to negate the need to load the entire ASCII grid into memory at once. The header will be loaded and will allow you to check the properties of the header. You can then either get specific values by index, coordinate or iterate over all points.

This library will build a cache of position the start of each row without reading the data to memory as you use any 'get' method. Therefore, for large files the first few 'get' calls may be slow but will increase as the structure of the file is mapped out and cached.

Usage:

use esri_ascii_grid::ascii_file::EsriASCIIReader;
let file = std::fs::File::open("test_data/test.asc").unwrap();
let mut grid = EsriASCIIReader::from_file(file).unwrap();
// Spot check a few values
assert_eq!(
    grid.get_index(994, 7).unwrap(),
    grid.header.no_data_value().unwrap()
);
assert_eq!(grid.get(390_000.0, 344_000.0).unwrap(), 141.270_004_272_460_937_5);
assert_eq!(grid.get(390_003.0, 344_003.0).unwrap(), 135.440_002_441_406_25);
assert_eq!(grid.get_index(3, 3).unwrap(), 135.440_002_441_406_25);
assert_eq!(grid.get_index(0, 0).unwrap(), 141.270_004_272_460_937_5);

// Interpolate between cells
let val = grid.get_interpolate(grid.header.min_x() + grid.header.cell_size()/4., grid.header.min_y() + grid.header.cell_size()/4.).unwrap();

// Iterate over every cell
let header = grid.header;
let grid_size = grid.header.num_rows() * grid.header.num_cols();
let iter = grid.into_iter();
let mut num_elements = 0;
for cell in iter {
    let Ok((row, col, value)) = cell else {
        panic!("your error handler")
    };
    num_elements += 1;
    if row == 3 && col == 3 {
        let (x, y) = header.index_pos(col, row).unwrap();
        assert_eq!(x, 390003.0);
        assert_eq!(y, 344003.0);
        assert_eq!(value, 135.44000244140625);
    }
    if row == 0 && col == 0 {
        let (x, y) = header.index_pos(col, row).unwrap();
        assert_eq!(x, 390000.0);
        assert_eq!(y, 344000.0);
        assert_eq!(value, 141.2700042724609375);
    }
}
assert_eq!(grid_size, num_elements);