Description

A Rust Crate which provides fast lookup of OSTN15 adjustments, for the conversion of ETRS89 grid coordinates to OSGB36, natively or via FFI.

Important

This library only provides the adjustment values. For a complete solution, see the lonlat_bng crate, which provides the OSTN15 transform via FFI, and / or the convertbng Python package.

Rust Crate Example

use ostn15_phf::ostn15_lookup;
// Caister Tower Eastings and Northings: 651307.003, 313255.686
let e_grid = (651307.003 / 1000.) as i32;
let n_grid = (313255.686 / 1000.) as i32;
let key = e_grid + (n_grid * 701) + 1
// key is 220065
// don't use unwrap() in production
let result = ostn15_lookup(&key).unwrap();
// result should be (102.787, -78.242, 44.236)
assert_eq!(result, (102.787, -78.242, 44.236));

FFI Examples

Python

import sys, ctypes
from ctypes import c_int32, c_double, Structure


class GridRefs(Structure):
    _fields_ = [("eastings", c_int32),
                ("northings", c_int32)]

    def __str__(self):
        return "({}, {})".format(self.eastings, self.northings)


class Shifts(Structure):
    _fields_ = [("x_shift", c_double),
                ("y_shift", c_double),
                ("z_shift", c_double)]

    def __str__(self):
        return "({}, {}, {})".format(self.x_shift, self.y_shift, self.z_shift)


prefix = {'win32': ''}.get(sys.platform, 'lib')
extension = {'darwin': '.dylib', 'win32': '.dll'}.get(sys.platform, '.so')
lib = ctypes.cdll.LoadLibrary(prefix + "ostn15_phf" + extension)

lib.get_shifts_ffi.argtypes = (GridRefs,)
lib.get_shifts_ffi.restype = Shifts

result = GridRefs(651, 313)

print(lib.get_shifts_ffi(result))

C

// compile with e.g. `clang -lostn15_phf -L target/release -o ostn15_shifts src/ostn15.c` from project root
// run with `LD_LIBRARY_PATH=target/release ./ostn15_shifts` from project root
#include <stdio.h>
#include <stdint.h>
#include <math.h>

typedef struct {
  int32_t easting;
  int32_t northing;
} gridrefs;

typedef struct {
  double x_shift;
  double y_shift;
  double z_shift;
} adjustment;

extern adjustment get_shifts_ffi(gridrefs);

int main(void) {
  // Caister Tower example: 651307.003, 313255.686
  // Convert to grid coordinates by dividing by 1000
  gridrefs initial = { .easting = 651, .northing = 313 };
  adjustment adj = get_shifts_ffi(initial);

  // Check if the lookup was successful (NAN indicates failure)
  if (isnan(adj.x_shift) || isnan(adj.y_shift) || isnan(adj.z_shift)) {
    fprintf(stderr, "Error: Grid reference lookup failed\n");
    return 1;
  }

  // Print the adjustment values
  // Expected result: (102.787, -78.242, 44.236)
  printf("Adjustment shifts: (%.3f, %.3f, %.3f)\n",
         adj.x_shift, adj.y_shift, adj.z_shift);

  return 0;
}

Building the Shared Library

• Ensure that Rust is installed
• Clone this repo
• In the repo root, run cargo build --release
• The dylib or DLL will be available as target/release/libostn15_phf.{dylib, dll}
• If you need to build a .so for Linux:
  1. ar -x target/release/libostn15_phf.a
  2. gcc -shared *.o -o target/release/libostn15_phf.so

License

MIT

This software makes use of OSTN15 data, which is © Crown copyright, Ordnance Survey and the Ministry of Defence (MOD) 2016. All rights reserved. Provided under the BSD 2-clause license.