The decorator's own venue photo becomes a true-scale wall β with every guardrail and every honesty note the app ships.
Mark four corners of a rectangle whose true size you know β a door frame, a panel β and the photo's wall maps to true size through a normalised DLT, the math ported from Laser Bench and tested. The guardrails refuse the bad inputs: crossed marks, a view nearly edge-on (a corner sine under 0.04), marks closer than 8 px, marks too small. Two marks only give a scale β right for a wall photographed straight on, not for perspective.
The garland's centre line is drawn on the photo; the mockup turns it into a centripetal CatmullβRom spline (Ξ± = 0.5) β no cusps, no self-loops within a segment. The length samples densely (32 steps a segment; a quarter circle lands within 0.5%). Then the honesty the app insists on: decor stays out of the 18 inches below a sprinkler β NFPA 13's strictest obstruction band β and your venue or fire marshal may require more.
Each balloon draws at half its diameter times the map's local scale at its centre; the centres scatter across a band as wide as the largest balloon, the small balloons drawn on top β the app's convention for how organic garlands look. The colour read: sample the client's swatch, convert sRGB β Lab with the D65 white, rank by CIEDE2000 (<2 reads same, <5 close, <12 similar), white-balance the photo's cast first. The honesty line: no predicted colour for double-stuffed combos β no validated model exists, so the app doesn't pretend.
| the mistake | what it costs |
|---|---|
| trusting two marks on an angled photo | a scale, not a map β the perspective lies; four marked corners for real walls |
| decor inside the sprinkler band | the obstruction rule the fire marshal quotes first; 18 in below the line is the floor |
| a colour matched to a double-stuffed prediction | no model exists; sample the real thing at the shop, promise the real thing |
The mockup screen walks the marks, draws the spline, scatters the balloons, and keeps the sprinkler band visible while you design; the colour match sits beside it with its bands and the white balance. The venue photo never leaves the device.
Every line here is the app's craft file: the mapping and its guardrails, the spline choice, the 18-inch band (NFPA 13, sourced), the scatter and the colour bands β each labelled sourced, derived or convention.