Surin Founding Father
The footprint in contact with the floor would appear to be 530mm x 1,330mm. However, as the 530mm marks a continuous line, I will assume that is the inside measurement of the bath. The dashed line, not dimensioned, is probably the widest point of the footprint. Perhaps the dashed line is another 10cm wider than the solid line. Therefore, the footprint for the bath would be in the order of 540mm x 1,330mm.
I sincerely enjoyed your astute observation, articulated analysis and basis for calculation.
The correct answer will be revealed at a later date.