Wael-lib NPM | npm.io

Well-Known Text Arithmetic Expression Language (WAEL)

The Well-Known Text Arithmetic Expression Language (WAEL) is an experimental, 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. Sections with an ⚠ experimental feature label indicate features that could be updated or modified in future versions.

Try out the language at geojsonscript.io with the WAEL code editor option selected.

Usage

Install dependency:

npm install wael-lib

Evaluate code using the evaluate() method:

import { Wael } from 'wael-lib';

const result = Wael.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 20x10 grid of points with 2-unit spacing starting from coordinates -110, 38:

Point(-110 38) + PointGrid(20, 10, 2)

Create the same grid and introduce random offsets:

Point(-110 38) + PointGrid(20, 10, 2)
    || Function(p => {
        xOffset = 1 - Math:random() * 2;
        yOffset = 1 - Math:random() * 2;
        p + Point(xOffset yOffset)
    })

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

PointGrid(20, 10, 4) | Rotate:bind(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 wael.ts script can be used to evaluate code and output the resulting WKT:

npx ts-node ./scripts/wael.ts --help

Following the build instructions, a wael binary application can be used:

wael --help

To evaluate code and output the resulting WKT, specify one or more input files:

wael ./myScript.wael

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

wael ./myScript.wael --geojson

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

wael -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.wael variables will be accessible to myFunctions.wael, and variables in both scripts will be accessible in the interactive environment.

wael ./myConstants.wael ./myFunctions.wael -i

Expressions can be passed in directly with the --evaluate (or -e) flag.

wael -e "Point(1 1) + Point(2 2)"

Any variables defined in the --evaluate script can be used in following script files. For example, the following path.wael script references an undefined start variable:

start ++ GeometryCollection(Point(2 2), Point(3 3), Point(4 4))

When evaluated with the following command:

wael -e "start = Point(1 1)" path.wael

The start variable will be defined in the --evaluate argument and the output will be:

GEOMETRYCOLLECTION (POINT (1 1), POINT (2 2), POINT (3 3), POINT (4 4))

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

⚠ experimental feature

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(Point(1 1)) ++ GeometryCollection(Point(2 2)); # GEOMETRYCOLLECTION(POINT (1 1),POINT (2 2))

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(Point(1 1)) ++ Point(2 2); # GEOMETRYCOLLECTION(POINT (1 1),POINT (2 2))

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. Supported data types include:

Number
Boolean: True, False
Geometry: Point, MultiPoint, LineString, MultiLineString, Polygon, GeometryCollection
Function

longitude = 2;              # number
bool = True;                # boolean
p = Point(longitude 3);     # geometry
fn = Function(p => p + 1);  # function

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)

Properties and Methods

Geometry properties and methods 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)

Geometry properties can be set by calling a method with an appropriate parameter. Since geometries are immutable, a new geometry instance is returned using the updated value:

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

Functions can have parameters bound using the bind() method:

Generate 10 Function(i => { x = Math:random() * 100; Point(x x) }) 
    || Round:bind(2)   

# GEOMETRYCOLLECTION (POINT (18.98 18.98), POINT (14.26 14.26), ...)

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)

Generate Expressions

⚠ experimental feature

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

⚠ experimental feature

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)

Each point in a geometry can be transformed using the pipe-all (|*) operator:

LineString(1.4325 1.5325, 2.23525 2.7453, 3.26474 3.34643) |* Round:bind(1) # LINESTRING (1.4 1.5, 2.2 2.7, 3.3 3.3)

Filtering

⚠ experimental feature

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

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

Reducing

⚠ experimental feature

Array-like geometries can be reduced using the reduce (|>) operator:

LineString(1 1, 2 2, 3 3) |> Function((total, current, index) => total + current) # Point(6 6)

Importing

⚠ experimental feature

Data can be imported using Import expressions. For example, if the file etna.wael contains Point(14.99 37.75), it can be imported using:

data = Import('etna.wael');
data # POINT (14.99 37.75)

Supported data formats include WKT, GeoJSON, and WAEL.

Built-In Functions

⚠ experimental feature

Several built-in functions are provided to support geometry generation and transformation.

`Math` proerties and methods

All JavaScript Math static properties and static functions are accessible from the Math variable:

pi = Math:PI;   # 3.141592653589793
Math:round(pi)  # 3

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), ... )

Rotate

Rotate(angleDegrees, originPoint, geometry) - rotate a geometry by the specified degrees around an origin point

Rotate(23, Point(0 0), MultiPoint(1 1, 2 2, 3 3)) # MULTIPOINT (1.3112079320509338 0.5297935627181312, ... )

Round

Round(precision, val) - round a number or Point coordinates with a given precision (defaults to 0)

Round(1, 1.255) # 1.3

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

To build the CLI binary, run:

npm run build-binary

The binary will be available at:

dist/bin/wael

Testing Instructions

npm test

Implementation Details

WAEL 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.

License

This project is made publicly available under the MIT license (see the LICENSE file).

wkt well-known text ohm dsl domain-specific language geospatial

@turf/turf chalk fs ohm-js tslib wellknown yargs

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Well-Known Text Arithmetic Expression Language (WAEL)

Usage

Examples

Terminal Usage

Syntax

Comments

Arithmetic

Concatenation

Variables

Functions

Properties and Methods

Conditional Expressions

Generate Expressions

Pipe Transformations

Mapping

Filtering

Reducing

Importing

Built-In Functions

Math proerties and methods

Flatten

PointGrid

PointCircle

Rotate

Round

ToX

Build Instructions

Testing Instructions

Implementation Details

License

`Math` proerties and methods