Wkt-lang NPM | npm.io

`wkt-lang`

wkt-lang is a domain-specific language for generating and manipulating geometry patterns. The language syntax aims to be a superset of Well-Known Text (WKT) with added support for programming features like variables, basic arithmetic, functions and comments. Geometries can be transformed using array programming features like geometry arithmetic and pipe transformations (see the Syntax section below for details).

Basic support is currently available for the following 2D geometries: POINT, LINESTRING, POLYGON, MULTIPOINT, MULTILINESTRING, GEOMETRYCOLLECTION.

🌍 Try out the language at geojsonscript.io with the wkt-lang code editor option selected.

Usage

Install dependency:

npm install wkt-lang

Evaluate code using the evaluate() function:

import { evaluate } from 'wkt-lang';

const result = evaluate(`Point(1 1) + Point(2 2)`);

See the Terminal Usage section for instructions using the CLI program.

Examples

The following examples use language constructs and built-in functions to generate geometry patterns.

Create a line of 10 points with 1-unit spacing:

Generate 10 Function(i => Point(i 0))

Create a 20x10 grid of points with 2-unit spacing starting from coordinates -110, 38:

Point(-110 39) + PointGrid(20, 10, 2)

Create the same grid but introduce random offsets:

Point(-110 39) +
    PointGrid(20, 10, 2) || 
    Function(p => {
        xOffset = 1 - random() * 2;
        yOffset = 1 - random() * 2;
        p + Point(xOffset yOffset)
    })

Rotate a 20x10 grid of points around origin by 23 degrees:

rotatePoint = Function((p, angle, origin) => {
    # Convert angle to radians
    angleRad = angle * (PI / 180);

    # Translate the point to the origin
    translatedX = p:x() - origin:x();
    translatedY = p:y() - origin:y();

    # Apply rotation
    rotatedX = translatedX * cos(angleRad) - translatedY * sin(angleRad);
    rotatedY = translatedX * sin(angleRad) + translatedY * cos(angleRad);

    # Translate the point back to the original position
    finalX = rotatedX + origin:x();
    finalY = rotatedY + origin:y();

    Point(finalX finalY)
});

PointGrid(20, 10, 4)
    || Function(p => rotatePoint(p, 23, Point(0 0)))

Create several nested circle polygons:

numRings = 5;
Generate numRings Function(i => {
    ring = numRings - i;
    (PointCircle((ring * 2), (ring * 10))) | ToPolygon
})

Terminal Usage

The wktl.ts script can be used to evaluate code and output the resulting WKT:

npx ts-node ./scripts/wktl.ts ./myScript.wktl

To output GeoJSON instead of WKT, add the --geojson flag:

npx ts-node ./scripts/wktl.ts ./myScript.wktl --geojson

To evaluate expressions interactively in a read-eval-print loop (REPL), use the --interactive (or -i) flag.

npx ts-node ./scripts/wktl.ts -i

All evaluated files, including the interactive environment, will share the same scope. This means that any variables defined in a script file will be accessible in following scripts and the interactive environment, if specified. For example, in the following command, myConstants.wktl variables will be accessible to myFunctions.wktl, and variables in both scripts will be accessible in the interactive environment.

npx ts-node ./scripts/wktl.ts ./myConstants.wktl ./myFunctions.wktl -i

Syntax

Define geometries using WKT syntax expressions:

GEOMETRYCOLLECTION(
    POINT (30 10),
    LINESTRING (30 10, 10 30, 40 40),
    POLYGON ((30 10, 40 40, 20 40, 10 20, 30 10)),
    POLYGON ((35 10, 45 45, 15 40, 10 20, 35 10),
        (20 30, 35 35, 30 20, 20 30))
)

Multiple expressions are separated by a semi-colon (;) and the last expression is returned after evaluation. For example, evaluating the code:

POINT (1 2);
LINESTRING (1 2, 3 4)

will result in LINESTRING (1 2, 3 4)

Expressions are white-space insensitive and case-insensitive, so the following syntax is also valid:

LineString (
    1  2 , 
    3  4
)

Comments

Comments begin with the # character:

# Napoli, Italy
Point(14.19 40.828)

Arithmetic

Coordinate values can be expressed using basic numeric arithmetic (+ - * / ^ %):

Point((8 * 3) (-12 + 5)) # POINT (24 -7)

Geometries also support basic arithmetic:

Point(1 2) + Point(3 4) # POINT (4 6)

Array-like geometries support array programming operations:

LineString(1 1, 2 2, 3 3) + LineString(10 10, 10 10, 10 10); # LINESTRING (11 11, 12 12, 13 13)
LineString(1 1, 2 2, 3 3) - Point(10 10); # LINESTRING (-9 -9, -8 -8, -7 -7)

Concatenation

Array-like geometries can be combined using the concatenate (++) operator:

LineString(1 1, 2 2) ++ LineString(3 3, 4 4); # LINESTRING (1 1, 2 2, 3 3, 4 4)
MultiPoint(1 1, 2 2) ++ MultiPoint(3 3, 4 4); # MULTIPOINT (1 1, 2 2, 3 3, 4 4)
GeometryCollection(1 1, 2 2) ++ GeometryCollection(3 3, 4 4); # GEOMETRYCOLLECTION(POINT (1 1),POINT (2 2),POINT (3 3),POINT (4 4))

Points can be appended to point array-like geometries:

LineString(1 1, 2 2) ++ Point(3 3); # LINESTRING (1 1, 2 2, 3 3)
MultiPoint(1 1, 2 2) ++ Point(3 3); # MULTIPOINT (1 1, 2 2, 3 3)
GeometryCollection(1 1, 2 2) ++ Point(3 3); # GEOMETRYCOLLECTION(POINT (1 1),POINT (2 2),POINT (3 3))

Non array-like geometries are concatenated into a GEOMETRYCOLLECTION:

Point(1 1) ++ Point(2 2); # GEOMETRYCOLLECTION(POINT (1 1),POINT (2 2))
Point(1 1) ++ Polygon((2 2, 3 3, 4 4, 2 2)); # GEOMETRYCOLLECTION(POINT (1 1),POLYGON ((2 2, 3 3, 4 4, 2 2)))

Variables

Variables are defined using the equal (=) operator:

longitude = 2;
latitude = 3;
Point(longitude latitude) # POINT (2 3)

Supported data types include:

number
boolean: true, false
Geometry: Point, MultiPoint, LineString, MultiLineString, Polygon, GeometryCollection

Properties and Methods

Geometry properties can be accessed using the accessor (:) operator:

p = Point(3 4);
p:type(); # Point
p:x(); # 3
p:y(); # 4

g = GeometryCollection(Point(1 2), Point(3 4));
g:type(); # GeometryCollection
g:numGeometries(); # 2
g:geometryN(1); # POINT (3 4)

l = LineString(1 2, 3 4);
l:type(); # LineString
l:numPoints(); # 2
l:pointN(1); # POINT (3 4)

Properties can be set by calling a method with an appropriate parameter:

p = Point(3 4);
p:x(5); # POINT (5 4)
p:y(6); # POINT (3 6)

Conditional Expressions

Boolean values True and False can be used in logical And, Or or negation ! expressions:

a = True;
b = False;
a And b; # False
a Or b; # True
!a; # False

Numeric values can be used in comparison expressions < <= > >= == !=, which return a boolean value:

a = Point(1 2);
b = Point(3 4);
a:x() < b:x() # true

Control flow can be dictated using If-Then-Else expressions:

result = If Point(1 2):x() < 3
         Then (LineString(1 1, 2 2, 3 3))
         Else (Point(0 0));
result # LINESTRING(1 1, 2 2, 3 3)

All three parts of the If-Then-Else expression are required. The Then and Else blocks can contain multiple lines, similar to a function body.

points = GeometryCollection(Point(0 0), Point(0 0), Point(0 0), Point(0 0), Point(0 0));
If (points:numGeometries() > 3) Then (
    a = Point(1 2);
    b = Point(3 4);
    a + b
) Else (
    a = LineString(1 1, 2 2);
    b = LineString(3 3, 4 4);
    a + b
) # POINT (4 6)

Functions

Functions are first-class and declared using the Function keyword:

getEquatorPoint = Function(longitude => Point(longitude 0));

They can be invoked using parentheses ():

getEquatorPoint(14.19) # POINT (14.19 0)

Functions can also accept multiple parameters and have function bodies spanning multiple lines. Similar to top-level expressions outside of a function, the last expression in the function body is used as the return value.

myFn = Function((x, y, last) => {
    first = Point(x y);
    LineString(first, last)
});

myFn(1, 2, Point(3 4)) # LINESTRING (1 2, 3 4)

Generate Expressions

Multiple geometries can be generated using the Generate expression by specifying an iteration count and either a geometry or a function that returns a geometry. The set of all geometries returned from a Generate expression are collected into a GEOMETRYCOLLECTION.

Generate 3 Point(0 0); # GEOMETRYCOLLECTION(POINT (0 0),POINT (0 0),POINT (0 0))
Generate 3 Function(x => Point(x x)) # GEOMETRYCOLLECTION(POINT (0 0),POINT (1 1),POINT (2 2))

The iteration count can also be specified as a variable:

count = 3;
Generate count Point(0 0) # GEOMETRYCOLLECTION(POINT (0 0),POINT (0 0),POINT (0 0))

Pipe Transformations

Mapping

The output from any expression can be used as the input to another function with the pipe (|) operator:

Point(1 1) | Function(x => LineString(x, 2 2)) # LINESTRING (1 1, 2 2)

Each item in an array-like geometry can be mapped using a function with the double-pipe (||) operator:

LineString(1 1, 2 2, 3 3) || Function(x => x * x) # LINESTRING (1 1, 4 4, 9 9)

The array map index is also available as function parameter:

LineString(1 1, 2 2, 3 3) || Function((x, i) => x * i) # LINESTRING (0 0, 2 2, 6 6)

Filtering

Array-like geometries can be filtered using the filter (|>) operator:

LineString(1 1, 2 2, 3 3) |> Function((x, i) => x:x() <= 2) # LINESTRING (1 1, 2 2)

Built-In Functions

Several built-in functions are provided to support geometry generation and transformation. Additionally, all JavaScript Math static properties and static functions are available in top-level variables.

Flatten

Flatten(g) - flatten all geometries in a GEOMETRYCOLLECTION.

Flatten(GeometryCollection(Point(1 1), GeometryCollection(Point(2 2)))) # GEOMETRYCOLLECTION(POINT (1 1),POINT (2 2))

PointGrid

PointGrid(x, y, spacing) - create a grid of points with the given X and Y count, and (optional) spacing

PointGrid(20, 10, 2) # GEOMETRYCOLLECTION(POINT (0 0),POINT (0 2), ... POINT (38 18))

PointCircle

PointCircle(radius, count) - create a circle of points with a given radius and point count.

PointCircle(5, 50); # GEOMETRYCOLLECTION(POINT (5 0),POINT (4.9605735065723895 0.6266661678215213), ... )

ToX

ToLineString(g), ToMultiPoint(g), ToPolygon(g), ToGeometryCollection(g) - convert an array-like geometry of points to a different geometry type

list = GeometryCollection(Point(1 1), Point(2 2), Point(3 3));
ToLineString(list); # LINESTRING (1 1, 2 2, 3 3)
ToMultiPoint(list); # MULTIPOINT (1 1, 2 2, 3 3)
ToPolygon(list); # POLYGON ((1 1, 2 2, 3 3, 1 1))
ToGeometryCollection(list) # GEOMETRYCOLLECTION(POINT (1 1),POINT (2 2),POINT (3 3))

Build Instructions

npm install
npm run build

Testing Instructions

npm test

Implementation Details

wkt-lang is implemented with TypeScript using Ohm. When code is evaluated, geometries are stored in an intermediate representation (IR) as GeoJSON objects, which can then be transformed to either WKT or GeoJSON as output.