Surveying
Every measurement carries error, and surveying is the discipline of arranging measurements so the errors cannot accumulate. These topics animate the error as it propagates, and the procedure that contains it.
Start from the beginning →8 topics you can watch now, 12 still to come.
Principles and chain surveying
The two principles every method in the subject obeys.
- Working from Whole to PartStart here. Survey the same plot both ways and watch one small error stay small and the other one grow all the way across the site.
- Errors and AdjustmentMore observations make a random error smaller and a systematic one no better — they just make you more confident about a wrong answer.
- Ranging, chaining and offsets
- Corrections for slope, temperature and sag
- Obstacles in chaining
Compass and traverse surveying
Direction as well as distance, and closing the loop.
- Bearings, meridians and local attraction
- Omitted measurements
Levelling and contouring
The vertical dimension, and how the ground is drawn.
- LevellingA level gives one thing — a horizontal line of sight. Everything after that is differencing readings, and equalising sight distances cancels two errors at once.
- Areas and VolumesWhere the survey becomes the number somebody is paid against — and where exact arithmetic on a sparse sample is arithmetic theatre.
- Instrument adjustments and the two-peg test
- Contouring methods in the field
Theodolite and tacheometry
Angles measured well enough to control a whole survey.
- Trigonometric levelling
- Stadia and tangential tacheometry
Curves and modern surveying
Setting out geometry, with instruments that do the arithmetic.
- Setting Out CurvesA circular curve demands that a driver turn the wheel instantaneously. The transition curve fixes the same problem a cam's motion law does, for the same reason.
- GNSS and Coordinate SystemsFour satellites, because the receiver's clock is the fourth unknown — and then a receiver reporting 10 mm precision on the wrong datum is 200 m out and confident.
- Compound and reverse curves
- Total station field procedures
- Remote sensing and GIS
About Surveying
Surveying is the discipline of knowing where things are precisely enough to build them, and it is organised around a principle that sounds procedural but is really about error: work from the whole to the part. Establish a few very accurate control points first, then fill in detail relative to them.
The reason is error propagation. Detail measured from control inherits only that control's error; detail measured from previous detail accumulates every error in the chain. That single ordering is what keeps a large survey consistent, and it explains most of the field procedure that follows.
Because error is unavoidable rather than a mistake, the subject treats it as a quantity to be distributed rather than eliminated. Adjustment methods spread a known misclosure across a network in a defensible way, which is why measuring more than the minimum is standard practice.
What to know first
- Trigonometry, and comfort with angles and bearings
- Basic error and averaging ideas
Where it gets used
- Setting out a building or road from design drawings
- Understanding what satellite positioning accuracy figures actually promise
- Computing areas and earthwork volumes from field measurements