Chainage & Stationing Calculator

Station text. The kilometre is split off first and the sub-kilometre remainder is rounded with integer arithmetic, never by formatting a float — which is why 999.9999 m prints as 1+000.000 and not 0+1000.000. Kilometre stations are written and read by the same rules as BTPL's CAD chainage tool, so a station on a drawing and one computed here agree, and a chainage typed into either tool is read the same way. Reading reverses the writing: a prefix such as CH, KM, STA or RD is separated from the number before the sign is read, so CH-1+050 is chainage 1050 and not minus 1050. That is why a negative chainage after a prefix ending in a letter is written with a space, CH -0+050. The separator may be +, - or /, so 1-050 and 1/050 are 1050, but a hyphen or slash between digits that is not followed by exactly three metre digits (two for 100-unit stations), such as the range 10-20, is refused rather than guessed at. A number with no separator is metres unless it is marked KM: KM 12.500 and 12.500 km are 12+500, the way Indian highway documents write kilometres, while CH 12.500 stays 12.5 m, because CH names a chainage, not a unit. A KM word between two numbers separates kilometres from metres, so 12 km 500 m is 12+500 and never 12,500 km. In text marked KM, a space before exactly three metre digits separates them too (KM 12 500). A road name or an identifier in front of the chainage is ignored: NH-48 Km 12.500 and NH-48 12+500 are both 12+500, and NH-48 1050 and a pier's P12 1050 are both 1+050. A name with a space before its number, such as Pier 12, is ignored before a bare number unless that number has exactly three metre digits: Pier 12 1050 is 1+050, but Pier 12 500 reads as 12+500, so write P12 500 for pier 12 at 500 m. Along the alignment, the centre line is treated as a polyline through the vertices you give. The chainage of a point is the distance to the foot of the perpendicular from it, its offset is that perpendicular distance, and the side is L or R looking along increasing chainage. A point past a bend, whose nearest point on the centre line is the vertex itself, is on the outside of the bend: left of a right-hand bend, right of a left-hand one. Stake-out pegs are set square to their leg; at a vertex, a peg on the inside of the bend goes to the corner of the two legs' offset lines, so it is the stated offset from both legs, and one on the outside is square to the incoming leg. Curved alignments are handled by supplying the curve as vertices — a chord every few metres is enough for setting out, but a true arc definition is not read yet, so a long curve given as two tangents will be short by the versine.