Technical GuidesKnowledge Base
Written for clients and field professionals — more guides are added as they are prepared.
UTM vs Latitude/Longitude
Latitude/longitude describes positions on the ellipsoid in degrees; UTM projects them onto a metric grid. Engineers work in UTM because distances and areas compute directly in metres — but every UTM coordinate is only meaningful with its zone and hemisphere stated. Rule of thumb: store and exchange geographic coordinates, design and compute in the projected grid, and always record the datum (WGS 84, Everest…) alongside either.
BTPL note: Convert between them with the free BTPL Coordinate Converter — 24 ellipsoids, DD/DM/DMS formats, bulk CSV/Excel.
DSM vs DTM
A Digital Surface Model records the first surface a sensor sees — treetops, rooftops, vehicles included. A Digital Terrain Model is the bare-earth ground after vegetation and structures are removed. Design happens on the DTM; the DSM serves clearance analysis, visibility studies and canopy assessment. The difference between the two is itself useful: canopy height and structure heights come from DSM minus DTM.
BTPL note: BTPL delivers both from UAV and LiDAR campaigns, with classification reviewed manually on critical areas.
GNSS vs DGPS vs RTK
GNSS is the umbrella — GPS, GLONASS, Galileo, BeiDou, NavIC. Standalone positioning is metre-class. Differential methods remove common errors using a reference station: post-processed static observation ('DGPS' in common Indian usage) achieves the highest, control-grade accuracy, while RTK delivers centimetre-class positions in real time for detail survey and stake-out. Which you need depends on the role: control demands static redundancy; production measurement runs on RTK verified against that control.
BTPL note: BTPL establishes control by static GNSS and densifies by RTK — with re-observation checks documented.
Understanding Drone Survey Accuracy
Accuracy in UAV mapping is engineered before takeoff: ground sampling distance sets the theoretical floor, ground control ties the block to the datum, and independent check points measure what was actually achieved (reported as RMSE). Be cautious of accuracy claims quoted without check-point verification — a beautiful orthomosaic can still be metres off datum if control was weak.
BTPL note: Every BTPL aerial deliverable ships with a check-point verification table.
