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GeoCAD Bridge Knowledge Center

Engineering Knowledge Center

Reference articles for surveyors, geodesists, GIS analysts and CAD engineers. Each article gives a short summary, the theory, a worked example with real numbers, common mistakes, FAQ and links to the tool that does the calculation.

Coordinate Systems 9 articles

Datums, projections, EPSG codes, UTM and national grids.

More coordinate systems topics (31)

Geodesy 6 articles

Reference frames, ellipsoids, datum transformations and grid shifts.

Surveying 16 articles

Traverse computation, adjustment, angles, bearings and survey QA.

More surveying topics (11)

Total Station 2 articles

Field procedures and reductions for total station work.

GPS / GNSS 3 articles

Static, RTK and network GNSS positioning.

RTK 1 article

Real-time kinematic positioning and quality control.

Leveling 1 article

Differential leveling, misclosure and height adjustment.

Construction Survey 1 article

Setting out, stakeout and as-built control.

GIS 1 article

Vector and raster analysis, data quality and web mapping.

More gis topics (29)

Mapping 3 articles

Map projections, scale and cartographic products.

CAD 0 articles

AutoCAD, Civil 3D, DXF/DWG exchange and drawing standards.

More cad topics (29)

File Conversion 0 articles

Moving data between CAD, GIS and GNSS formats.

More file conversion topics (26)

Country Coordinate Systems 3 articles

National grids and datums by country.

More country coordinate systems topics (40)

Glossary

Ain el Abd 1970
Ain el Abd 1970 : a geodetic datum with its origin at Ain el Abd (Saudi Arabia) on the International 1924 (Hayford) ellipsoid.
Angular misclosure
Angular misclosure : the measured angle sum minus the theoretical angle sum of a traverse, expressed in seconds of arc.
Axis order
Axis order : the order and direction of the axes of a coordinate reference system as defined by its authority.
Azimuth
Azimuth : the clockwise horizontal angle from a reference north direction to a line, between 0° and 360°.
Bowditch rule (compass rule)
Bowditch rule : a traverse adjustment in which the correction to each departure and latitude equals the total misclosure in that component multiplied by the leg length divided by the total traverse length, with opposite sign.
Closed traverse
Closed traverse : a traverse that starts and ends on points of known position, either the same point (loop) or different points (link).
Datum transformation
Datum transformation : a coordinate operation between two different geodetic datums, whose parameters are derived empirically and therefore carry an accuracy.
Differential leveling
Differential leveling : determining the height difference between points from horizontal sight readings on vertical staffs.
Distance reduction
Combined scale factor : the product of the elevation (height) factor and the grid scale factor, converting ground distances to grid distances.
Egypt 1907 datum
Egypt 1907 : the geodetic datum of Egypt’s classical triangulation, on the Helmert 1906 ellipsoid (a = 6 378 200 m, 1/f = 298.3).
EPSG:4326
EPSG:4326 : the geographic 2D coordinate reference system of the WGS 84 datum ensemble, axes latitude (north) and longitude (east) in degrees.
GNSS surveying
GNSS surveying : precise positioning using carrier-phase observations from global navigation satellite systems.
Grid shift transformation
Grid shift : a transformation that applies interpolated coordinate offsets from a regular grid of known differences between two datums.
KSA-GRF17
KSA-GRF17 : Kingdom of Saudi Arabia Geodetic Reference Frame 2017, a plate-fixed realization of ITRF2014 for Saudi Arabia on the GRS 80 ellipsoid.
Least squares adjustment
Least squares adjustment : an estimation method that minimizes Σ w·v², where v are observation residuals and w their weights (inverse variances).
Link traverse
Link traverse : a closed traverse that begins and ends on different points of known coordinates and orientation.
Open traverse
Open traverse : a traverse that does not close on a point of known position, so its accuracy cannot be computed from its own observations.
Quadrant bearing
Quadrant bearing : a horizontal direction stated as N or S, an angle up to 90°, then E or W.
Relative precision (precision ratio)
Relative precision : the ratio of linear misclosure to total traverse length, expressed as 1:(ΣL / misclosure).
RTK (real-time kinematic)
RTK : GNSS positioning that resolves carrier-phase integer ambiguities in real time using corrections from a reference receiver.
Stakeout (setting out)
Stakeout : physically marking the position of designed features on site from their coordinates.
Total station
Total station : an instrument that measures horizontal and vertical angles and slope distances electronically and computes coordinates.
Transit rule
Transit rule : a traverse adjustment in which each departure is corrected by −f E ·|ΔE i |/Σ|ΔE| and each latitude by −f N ·|ΔN i |/Σ|ΔN|.
Transverse Mercator projection
Transverse Mercator : a conformal cylindrical projection whose cylinder axis lies in the equatorial plane, so the line of true scale is a meridian.
Traverse adjustment
Traverse adjustment : the process of distributing the angular and linear misclosure of a traverse among its observations so that computed coordinates agree with fixed control.
UTM (Universal Transverse Mercator)
UTM : a global system of 60 Transverse Mercator zones, 6° wide, with scale factor 0.9996 on each central meridian, false easting 500 000 m and false northing 0 m (north) or 10 000 000 m (south).
UTM zone
UTM zone : one of 60 six-degree longitude bands, each with its own Transverse Mercator projection centred on its central meridian.
Web Mercator (EPSG:3857)
Web Mercator : a Mercator projection using spherical equations with radius 6 378 137 m applied to WGS 84 latitude and longitude.
WGS 84
WGS 84 : the World Geodetic System 1984, an Earth-centred, Earth-fixed reference system with its own ellipsoid, maintained by the US NGA.