Open the picture exactly as the app shows it (the same file). Coordinates are fractions of the picture: u = 0 left … 1 right, v = 0 top … 1 bottom. With "Width in metres" set, polygons are also printed in metres with y = 0 at the top edge and negative toward the bottom, the way src/config/plan.ts stores rooms.

Copy the lines you need into src/config/*.ts (house.ts: WINDOWS boxes, ENERGY_AT, CAT_PERCH; garden.ts: GARDEN_LIGHTS at; plan.ts: GROUND pts).