Survey of Bangladesh (SOB) Datum Integration
All ground surveys, bathymetric soundings, UAV photogrammetry, and civil engineering drawings are calibrated to the National Everest 1830 (Modified) ellipsoid and BGD2000 geodetic datum, guaranteeing zero coordinate drift and 100% legal defensibility.
Official National Geodetic Baseline Parameters
Using uncalibrated localized coordinate systems causes severe spatial clashes during construction. We anchor all linear and vertical infrastructure to statutory Survey of Bangladesh (SOB) transformation parameters.
| Geodetic Parameter | Survey of Bangladesh (SOB) Reference Value |
|---|---|
| Reference Ellipsoid | Everest 1830 (Modified) |
| Semi-Major Axis (a) | 6,377,276.345 meters |
| Semi-Minor Axis (b) | 6,356,075.413 meters |
| Inverse Flattening (1/f) | 300.8017 |
| Projection System | Bangladesh Transverse Mercator (BTM) |
| Central Meridian | 90° 00' 00" East |
| Latitude of Origin | 0° 00' 00" (Equator) |
| Scale Factor at Origin | 0.9996 |
| False Easting / Northing | 500,000 m Easting / 0 m Northing |
| Vertical Datum Reference | Survey of Bangladesh Mean Sea Level (MSL) / PWD Datum (+0.46m offset) |
Six Pillars of Survey Precision & Verification
How every field observation, GNSS baseline, and engineering drawing transitions through systematic verification before client sign-off.
Survey Accuracy & GCP Verification
Dual-frequency carrier-phase ambiguity resolution, multi-constellation cycle-slip screening, and mathematical loop closure against Survey of Bangladesh primary GTS pillars.
- Pre- and post-marking for photogrammetry and aerial drone flights
- Ground Control Point (GCP) static and RTK verification grids
- Independent check of tribrach calibration and antenna phase center offsets
Coordinate & Elevation Checks
Closed-loop digital leveling runs with Sokkia B 20A and Topcon AT B 3 automatic optical levels, holding elevation errors strictly below < 5mm √K.
- Permanent Benchmark (BM) and Temporary Benchmark (TBM) monumentation
- Double-run leveling closure checks across road and bridge alignments
- Rigorous geoid model separation and ellipsoidal-to-orthometric height conversion
Data Validation & Quality Control
Independent checkpoints (CPs)—never used during UAV aerotriangulation or bundle adjustment—to audit digital surface models (DSM/DTM).
- Root-Mean-Square Error (RMSE) calculation independently across X, Y, and Z
- ASPRS Class 1 accuracy verification (< 2.5cm/pixel ground sample distance)
- Point cloud outlier filtering, classified ground surface extraction, and contour sanity checks
Standards & Specification Compliance
Full alignment with Bangladesh National Building Code (BNBC), AASHTO highway design manuals, and IHO S-44 hydrographic standards.
- Hydrological scouring and high-flood level (HFL) calibration for bridges
- Hydrographic bathymetric sounding uncertainty < ±0.15m (IHO Special Order)
- Statutory building setback and Rajuk / DNCC zoning compliance
Positional Accuracy Assessment
Coordinate transformation checks between local grid, BTM, and WGS84 UTM Zone 45N/46N to eliminate boundary overlap and GIS layer displacement.
- Rigorous Helmert 7-parameter coordinate transformation testing
- Cadastral mouza sheet geo-rectification and boundary alignment
- Road corridor chainage stationing validation against RHD/LGED databases
Final Map & Stamped Engineering Sign-Off
Comprehensive multi-disciplinary review by our Lead Surveyors, QA/QC Engineers, and Chief Structural Engineer prior to official release.
- Signed and stamped drawings legally admissible for government departments
- Deliverables formatted in native DWG, GeoTIFF, LAS/LAZ point cloud, and Shapefiles
- Archival of raw RINEX, field notes, and adjustment logs for long-term auditability
Keep in touch
From corridor surveying to UAV photogrammetry and spatial databases, reach our engineering team for technical consultation and deployment.
Geospatial Works Ltd.
64/1 (D1), Lake Circus, Kalabagan, Dhaka 1205