S+SNZ Geodetic Survey cheat sheet

Cadastral survey defines parcel boundaries and rights in land; the survey record (plan, CSD, dataset) is the legal evidence, not the field marks alone.

Boundary reinstatement hierarchy: undisturbed original marks, then original plan measurement, then occupation, then abutting parcel evidence; later surveys cannot override undisturbed originals.

Acceptable misclose for a rural boundary traverse is typically 1:5000 or better; urban cadastral traverses commonly require 1:2000 to 1:5000, per jurisdiction standard.

Terrestrial cadastral marks are commonly required within 0.01-0.05 m of true position; GNSS-derived cadastral positions are often accepted at 0.02-0.10 m depending on class.

New Zealand cadastral classes: survey network marks (SO/PRN), boundary marks, and non-boundary marks; boundary marks must be placed at every defined corner unless exempted.

Adverse possession and boundary encroachment are legal questions; the surveyor reports measurement evidence and does not adjudicate title.

Parcel area is computed from the adjusted boundary coordinates (plane or projection), not from unadjusted field observations; note the projection and scale factor used.

Easements and limited-title interests are shown as encumbrances on the plan; their position must be surveyed to the same accuracy as the parent boundary.

GNSS position accuracy depends on geometry (DOP), signal quality, and baseline length; PDOP above about 6 degrades RTK fix quality materially.

RTK/network RTK typical horizontal accuracy is 0.01-0.03 m + 1 ppm; static GNSS baselines can reach 0.005 m + 1 ppm after rigorous adjustment.

Scale factor: grid distance = ground distance x combined scale factor (point scale x elevation factor); elevation factor = R/(R+h).

Total station horizontal angle standard deviation is typically 1-5 arcseconds; distance accuracy typically 1-2 mm + 1-2 ppm.

Traverse misclose ratio = total linear misclose / total traverse length; angular misclose is distributed by Bowditch or transit method before linear adjustment.

Leveling loop misclose limit is commonly 4-12 mm x sqrt(km) for ordinary differential leveling; precise leveling uses tighter specifications.

Coordinate transformation between datums requires a published 7-parameter (Helmert) or grid-based model; a 2-parameter shift is invalid over large areas.

Redundancy in a network is assessed via the redundancy number; low redundancy means an undetected blunder is likely to pass the adjustment.

IHO S-44 order accuracy (95% confidence): Special 0.25 m, Order 1a 0.50 m, Order 1b 0.50 m, Order 2 1.00 m total vertical uncertainty.

Sounding density must resolve the smallest feature of concern; S-44 requires full seafloor coverage for Special and Order 1a areas.

Chart datum is normally Lowest Astronomical Tide (LAT); soundings are reduced to chart datum, and tide reduction errors propagate directly into depth error.

Sound velocity errors cause refraction; a 1 m/s sound-velocity error over 100 m depth can produce decimeter-scale depth error, so regular casts are required.

Multibeam coverage requires overlap between adjacent swaths (commonly 10-20%) and adequate along-track ping density to meet object detection.

Positioning for hydrography commonly uses RTK or PPK GNSS with 0.1-0.5 m horizontal accuracy; vertical accuracy governs sounding uncertainty.

Total propagated uncertainty (TPU) combines position, tide, sound velocity, and beam-angle uncertainty; S-44 compliance is assessed against TVU at 95%.

Feature detection: side-scan sonar and multibeam backscatter support object detection; single-beam echosounders cannot guarantee full coverage.

Setting-out tolerances are project-specific; typical structural steel column positions are held to 3-5 mm, while earthworks are held to 20-50 mm.

Vertical control for construction is often transferred by leveling from a benchmark; a single benchmark should be checked against a second before setting out.

Machine control and GPS-guided grading rely on a site calibration (localization) to a project datum; the calibration must be verified by independent checkpoints.

As-built surveys compare constructed features to design; deviations beyond tolerance are reported to the engineer, not corrected by the surveyor.

Horizontal curves: tangent length T = R tan(Δ/2); curve length L = RΔ (radians); external E = R(sec(Δ/2) - 1).

Vertical curves: rate of change of grade k = L/A; the curve length L = kA where A is the algebraic grade change in percent.

Earthwork volumes from cross-sections use the average end area method or prismoidal formula; prismoidal is more accurate for varying sections.

Deformation monitoring uses repeated precise leveling or total station/ GNSS with fixed reference points; movement is assessed against a stated confidence interval.

Subdivision design balances lot yield, road hierarchy, and servicing; minimum lot size and frontage are set by the local district plan, not by the surveyor.

Road classification hierarchy (arterial, collector, local) governs width, gradient, and intersection spacing; typical local road reserve is 15-20 m.

Longitudinal road gradients commonly limited to 8-12% for vehicle access; steeper grades require specific design approval.

Stormwater design uses the rational method Q = CiA for small catchments; time of concentration and return period (e.g., 10-year) must be stated.

Servicing corridors (water, wastewater, power, telecommunications) require vertical and horizontal separation; minimum cover and separation are set by utility standards.

Urban design principles include legibility, connectivity, and passive surveillance; these inform block layout and street frontage rather than survey measurement.

Earthworks balance cut and fill to minimize cartage; a balanced site reduces cost but must respect geotechnical and drainage constraints.

Legalisation of roads and reserves follows subdivision approval; the survey plan must show the new boundaries and any land to be vested.

Coordinate reference systems: a datum defines the origin and orientation; a projection maps the ellipsoid to a plane; EPSG codes identify both.

Common NZ projections: NZGD2000 / New Zealand Transverse Mercator (NZTM2000, EPSG:2193); geographic coordinates use EPSG:4167.

Horizontal accuracy of GIS data is reported as RMSE or at 95% confidence; metadata must state the accuracy and the source.

Topology rules (no gaps, no overlaps, no dangling nodes) enforce spatial integrity in a geodatabase; violations are corrected before analysis.

Vector data models: points, lines, polygons; raster uses a grid of cells with a cell size that sets spatial resolution.

Spatial joins and overlays (intersect, union, clip) depend on consistent CRS; reprojection introduces error and should be done once, deliberately.

Metadata standards (e.g., ISO 19115) record lineage, accuracy, and currency; a dataset without lineage cannot be reliably assessed for fitness.

GNSS-derived GIS positions are commonly 1-5 m with autonomous positioning; survey-grade GIS requires correction services or post-processing.