kataho_code

Flutter package for converting between coordinates, Nepal-focused 11-character Plus Codes, human-readable Kataho Codes, and KIDs — in any direction.

latitude/longitude   27.7172, 85.3240
Plus Code            7MW4JQF6+62R
Kataho Code          १९ माणिक प्रकाश ००७५
KID                  192451960075

Give the package any one of the four and it returns all of them. It includes encrypted geocode datasets, model classes, an async repository, a KatahoCodeCubit, and a ready-to-use KatahoCodeBuilder.

Installation

dependencies:
  kataho_code: ^0.3.0

Then run flutter pub get.

Encryption key

The package does not contain the AES key. Every consumer must provide the Base64-encoded 32-byte key that matches the encrypted datasets. Keep this key in a secret build configuration and never commit it to source control.

For example:

flutter run --dart-define=KATAHO_AUTH_KEY=<base64-aes-key>

Widget usage

KatahoCodeBuilder accepts a Plus Code, a Kataho Code, coordinates, or — when the input type is not known ahead of time — a free-form input:

// From a Plus Code
KatahoCodeBuilder(
  plusCode: '7MV7P8CF+J68',
  authKey: const String.fromEnvironment('KATAHO_AUTH_KEY'),
  builder: (context, code) => Text(code.display),
  placeholder: const Text('Loading...'),
)

// From coordinates
KatahoCodeBuilder(
  latitude: 27.7172,
  longitude: 85.3240,
  authKey: const String.fromEnvironment('KATAHO_AUTH_KEY'),
  builder: (context, code) => Text(code.formattedPlusCode),
  placeholder: const Text('Loading...'),
)

// From a Kataho Code
KatahoCodeBuilder(
  katahoCode: '१९ माणिक प्रकाश ००७५',
  authKey: const String.fromEnvironment('KATAHO_AUTH_KEY'),
  builder: (context, code) => Text('${code.latitude}, ${code.longitude}'),
  placeholder: const Text('Loading...'),
)

// From a KID
KatahoCodeBuilder(
  kid: '192451960075',
  authKey: const String.fromEnvironment('KATAHO_AUTH_KEY'),
  builder: (context, code) => Text(code.display),
  placeholder: const Text('Loading...'),
)

// Anything the user typed
KatahoCodeBuilder(
  input: userText,
  authKey: const String.fromEnvironment('KATAHO_AUTH_KEY'),
  builder: (context, code) => Text(code.display),
  placeholder: const Text('Loading...'),
)

Provide exactly one of plusCode, katahoCode, kid, input, or latitude + longitude.

The result

Every lookup returns a KatahoCode carrying all four representations, so one conversion covers every direction:

code.display           // '१९ माणिक प्रकाश ००७५'  Devanagari
code.displayLatin      // '19 माणिक प्रकाश 0075'  Western digits
code.plusCode          // '7MW4JQF662R'          normalised
code.formattedPlusCode // '7MW4JQF6+62R'         canonical
code.kid               // '192451960075'
code.latitude          // 27.7172
code.longitude         // 85.3240
code.segmentedPlusCode // '7MW4-JQF6-62R'        for debugging

latitude and longitude are the centre of the area the Plus Code names — an 11-character code covers roughly 3.5m x 2.8m.

Repository usage

Use GeocodeRepository directly when the application owns loading and state. resolve detects the input type for you:

final repository = GeocodeRepository(
  authKey: const String.fromEnvironment('KATAHO_AUTH_KEY'),
);

await repository.resolve('7MW4JQF6+62R');        // Plus Code
await repository.resolve('१९ माणिक प्रकाश ००७५');  // Kataho Code
await repository.resolve('192451960075');        // KID
await repository.resolve('27.7172, 85.3240');    // coordinates

Or call a direction explicitly:

await repository.katahoCodeFor('7MW4JQF6+62R');
await repository.katahoCodeForLatLng(27.7172, 85.3240);
await repository.katahoCodeForDisplay('१९ माणिक प्रकाश ००७५');
await repository.katahoCodeForKid('192451960075');

Every one returns the same KatahoCode?, null when the input is unrecognised or has no mapping. Call await repository.preload() during startup to decrypt and cache all datasets before the first lookup.

Plus Codes without the datasets

plusCodeFromLatLng and plusCodeToArea are standalone and need no encryption key:

final code = plusCodeFromLatLng(27.7172, 85.3240); // '7MV7P88F+VJC'

final area = plusCodeToArea('7MV7P88F+VJC')!;
area.latitude;    // centre latitude
area.longitude;   // centre longitude
area.latitudeLo;  // bounding box edges

plusCodeToArea returns null for a short/relative code such as 8CF+J68, which cannot be decoded without a reference location.

Input format

Plus Codes may contain the standard separator, spaces, or hyphens, in any case. The repository normalises them and expects 11 significant characters.

Kataho Codes are matched leniently: digits may be Devanagari (०९) or Western (09), house numbers may be unpadded (0 for 0000), and each segment also matches the hints recorded in the datasets, so a romanised 9 laxya niwas 1838 resolves too.

KIDs are exactly 12 digits with no separators, in Devanagari or Western script. The layout is fixed-width, so it parses unambiguously:

19   245   196   0075
└ region    └ word halves   └ house number
     JQ->245  F6->196

The two 3-digit word groups come from splitting the 4-character word segment of the Plus Code (JQF6 -> JQ + F6) and mapping each half through geocode_word_kids.

Coordinates are accepted as "lat,lng" or "lat lng".

A lookup returns null for invalid input or an unmapped code.

Data tooling

The scripts in tool/ are for dataset administrators who have the encryption key. See tool/README.md before decrypting or re-encrypting the assets.

License

MIT. See LICENSE.