Chapter 1 recap
Where GIS fits
The key takeaways from this chapter’s 2 lessons.
GIS on linear projects
- Linear projects cross land, networks and constraints that are managed in GIS by many owners.
- GIS holds the corridor (land, consents, environment, utilities); BIM holds the structures and systems built in it.
- Each GIS layer needs a source, a date, a coordinate system and a stated accuracy.
- IFC 4.3 brings alignments and infrastructure into open BIM, so the two can meet on one reference.
Alignments and chainage
- An alignment is a horizontal line (straights, curves, transitions) plus a vertical profile (grades and vertical curves).
- Chainage or stationing is the distance along it; offsets are left or right of it.
- US stations are written in hundreds of feet (Sta. 5+10 = 510 ft); metric chainage in kilometres and metres (Ch 1+250).
- A chainage only means something with its alignment name and revision; IFC 4.3 carries alignments as IfcAlignment.