Grid Dates Interpolation

When a Haulage Rule takes its terrain from a Grid Folder, each grid is a surface at one point in time. The date comes from the last 10 characters of the grid's name, for example: Topo_2026-02-01

Option	1 Jan grid	1 Feb grid	1 Mar grid	Meaning
Start Date	1 Jan -> 1 Feb	1 Feb -> 1 Mar	1 Mar -> 1 Apr	The date in the name is when that surface starts applying. It stays in force until the next grid.
Middle Date (Default)	1 Jan -> 16 Jan	-16 Jan -> -15 Feb	-15 Feb -> 1 Apr	The date is the centre of its period. Switches happen halfway between neighbouring grids.
End Date	None (zero width)	1 Jan -> 1 Feb	1 Feb -> 1 Apr	The date is when that surface is reached. The grid covers the period that leads up to its date.