API & Deep Linking

No API key required

All calculations run entirely in the browser. There is no server-side API, no authentication layer, and no usage quota. Every URL you construct and every JavaScript call you make runs the same engine that powers the interactive calculator.

URL Parameters

Append parameters to https://www.class4steel.com/ to pre-load a specific cross-section. The calculator reads the parameters on page load, generates the polygon, runs the calculation, and renders the full results — no user interaction required.

Two modes are available: arbitrary vertex list and parametric preset.

Arbitrary polygon — ?pts=

Pass a flat comma-separated list of x,y coordinate pairs. The engine closes the polygon automatically. Minimum 3 vertices. Both clockwise and counter-clockwise winding are accepted.

Syntax

Examples

Standard profiles — ?preset=

Call any built-in parametric profile by name. Override individual dimensions via additional URL parameters. Any omitted parameter falls back to its built-in default value, so you only need to specify what differs. Fillet radii are applied automatically when supported by the profile.

Syntax

Examples

Presets & parameters

All dimension values are in the same unit system as the coordinate input (mm, cm, or any consistent unit).

g highlighted in amber — see Gap parameter note below.

Global interface — window.class4steel

When the calculator page is open, the engine exposes a global object window.class4steel that allows external scripts (browser console, injected scripts, iframe postMessage bridges) to inject geometry and retrieve results programmatically.

Methods

// Set vertices and trigger calculation
const results = window.class4steel.setVertices([
  { x: 0,   y: 0   },
  { x: 100, y: 0   },
  { x: 100, y: 200 },
  { x: 0,   y: 200 }
]);

// Retrieve the last computed result without recalculating
const cached = window.class4steel.getResults();

setVertices(array) — accepts an array of {x, y} objects, updates the vertex table, runs the calculation engine, renders the polygon and results, and returns the result object synchronously.

getResults() — returns the last computed result object without triggering a new calculation. Returns null if no calculation has been run yet.

Returned properties

Both setVertices() and getResults() return the same object:

Integration examples

Console / DevTools

// Open class4steel.com, then in DevTools console:
const r = window.class4steel.setVertices([
  {x:0, y:0}, {x:120, y:0}, {x:120, y:14},
  {x:59, y:14}, {x:59, y:186}, {x:120, y:186},
  {x:120, y:200}, {x:0, y:200}, {x:0, y:186},
  {x:61, y:186}, {x:61, y:14}, {x:0, y:14}
]);

console.log(`Area:  ${r.area.toFixed(2)} mm²`);
console.log(`Ix:    ${r.Ix.toFixed(0)} mm⁴`);
console.log(`Wpl,x: ${r.Wpl_x.toFixed(0)} mm³`);

Iframe integration

<!-- Embed a pre-calculated section directly -->
<iframe
  src="https://www.class4steel.com/?preset=isection&B=100&H=200&tf=14&tw=8"
  width="100%"
  height="700"
  style="border:none"
  title="I-beam HEB200 section properties"
></iframe>

Generating a shareable link from your application

function buildClass4SteelURL(vertices) {
  const flat = vertices.flatMap(v => [v.x, v.y]).join(',');
  return `https://www.class4steel.com/?pts=${flat}`;
}

function buildClass4SteelPresetURL(presetId, params) {
  const qs = new URLSearchParams({ preset: presetId, ...params });
  return `https://www.class4steel.com/?${qs}`;
}

// Examples:
buildClass4SteelURL([{x:0,y:0},{x:100,y:0},{x:50,y:80}]);
// → "https://www.class4steel.com/?pts=0,0,100,0,50,80"

buildClass4SteelPresetURL('isection', {B:100, H:200, tf:14, tw:8});
// → "https://www.class4steel.com/?preset=isection&B=100&H=200&tf=14&tw=8"

Hollow sections & stitching seams

Profiles like rect_tube, circ_tube, double_l_btb and the star variants simulate internal voids by generating a continuous polygon with a stitching seam — a zero-width cut that connects the outer and inner contours.

This allows the Shoelace / surveyor integration to treat hollow sections as a single closed polygon without modifying the core mathematical engine. The seam introduces no geometric error: the two edges of the seam are co-linear and cancel out in the area integral.

The g gap parameter

The g parameter is unique to the double and quad angle presets. It defines the clear distance between the back-to-back webs, typically used to account for:

• The thickness of a gusset plate between the angles
• The thickness of a packing plate (presilla)
• A physical gap required for bolted connections

Use g=0 for angles in direct contact (theoretical case, common in welded assemblies). The stitching seam connecting the two contours has a width of 1×10⁻⁴ units regardless of g, which is negligible relative to any practical section dimension.

// g=10 → each web is offset 5 mm from the centroidal axis
https://www.class4steel.com/?preset=double_l_btb&B=80&H=120&tf=12&g=10&r=10&r1=5