The idea
Build the cross-section from nodes (points) and the
lines / arcs / circles that connect them. The solver computes its
area, centroid, moments of inertia, and section modulus values. Any closed loop you
draw inside another closed loop is treated as a hollow cut-out
automatically — you never have to "close" a shape by hand.
Skipping the drawing — the scanner
Tap Open scanner in the sidebar, photograph or upload the
cross-section from your textbook, and the AI builds the geometry for you. Make
sure the dimension labels (B, H, t, r) are visible and readable. Use the
Nodes and Edges & curves panels to fix any
dimensions the AI got wrong.
The five tools
- Node V — tap empty space to place a point, or tap an
existing node / edge / curve to select it. Then use 🗑 Delete
selected (or the Delete key) to remove it.
- Line L — tap a node (or empty space to drop one),
then tap the next node to connect them with a straight edge. Keep tapping to
chain around the perimeter; the shape closes itself when you return to the start.
- Arc A — tap the start node, then a point the curve
passes through, then the end node. Arcs are circular only — the
app splits them into circles, semicircles, quarter-circles, or sectors. It does
not handle parabolas, ellipses, or other curves.
- Circle C — tap the centre, then any point on the
circumference (or type the radius and press Enter).
- Set Origin O — tap the point you want as (0, 0).
Use it after drawing so you can read x̄ and ȳ from any reference corner.
Solid vs. hollow
You don't tag anything — the app looks at how loops are nested.
- A loop not inside any other loop → solid.
- A loop inside one other loop → hollow (subtracted).
- A loop inside two others → solid again (an island inside a hole).
The shaded blue area is the solid part. The unshaded interior of a nested loop is
the hollow part.
Typing exact distances (works on phones too)
The Distance + Angle panel above the canvas is the primary way to
enter precise dimensions.
- Distance only — type the length, leave Angle blank. The line goes
from the last point toward wherever the cursor is pointing, at exactly that length.
Useful for axial segments (combine with Ortho).
- Distance + Angle — type both. The line goes at exactly that angle
(0° = right / +X axis, 90° = up / +Y axis, counter-clockwise positive) for that
length. Polar entry, like AutoCAD's
@dist<angle.
- Tap Apply (or press Enter while a field is focused) to commit.
On desktop you can also just type digits on the canvas — the distance field fills
automatically. Hit Enter or click to commit.
- Hold Shift for one-off Ortho, or click the Ortho
button (or press F8) to lock it on.
Point labels & editing
Every node you place gets an automatic label (A, B, C, …). Use the
Nodes panel to change a node's exact (X, Y) — every edge
connected to it follows along automatically. Use Edges & curves
to set a line's length numerically (the end node slides along the existing direction)
or a circle's radius, and to delete any single edge or curve. You can also tap a
node/edge/curve on the canvas with the Node tool to select it, then
Delete.
Navigating the canvas
- Pan — hold the middle mouse button and drag on a
desktop, or use a two-finger drag on a phone or tablet.
- Zoom — mouse wheel on a desktop, pinch on touch, or
the + / − buttons.
- Fullscreen — tap the ⛶ Full button on the canvas
toolbar to expand the drawing area to the whole screen. Tap again or press
Esc to exit.
- The X and Y coordinate axes start hidden. They appear after you use
Set Origin so the coordinate system reflects the reference point you chose.
You can toggle them in Grid & display.
Tips
- Lines and arcs chain together: an arc continues from the last
point of the previous segment, so you can mix straight edges and curved fillets in
one continuous loop.
- Use Type exact point (X, Y) to place a node at exact
coordinates — then switch to Line to connect it to others.
- Snap to grid is on by default. Turn it off in Grid & display
for fine adjustments.
- Press Esc to cancel the current sketch, Enter to close it.
