Getting off base while staying on point with mobile mapping

Mapping made baseless

Mobile mapping has long been tethered to the ground. For years, achieving centimeter-level absolute accuracy required the logistical headache of establishing local base stations. While methods such as single base, Trimble® Applanix SmartBase® and multi-single base served as the industry standards, they carried hefty hardware costs and deployment constraints.

Enter Trimble’s POSPac Post-Processed CenterPoint RTX® (PP-RTX). This cloud-based global GNSS correction service leverages Trimble’s worldwide tracking network to deliver survey-grade accuracy without a local base station. The latest evolution, IN-Fusion+® GNSS-Inertial integration technology, handles multi-frequency and multi-satellite constellations — including Beidou-III — to slash convergence times and boost reliability.

To prove PP-RTX can truly replace legacy workflows, a rigorous benchmark test was conducted in Biberach, Germany.

Testing the terrain

The open-sky test site, situated in an industrial zone, hosted three separate mobile mapping missions. Each mission consisted of three 1.2-kilometer loops managed by a Trimble MX60 mobile mapping system. The vehicle was equipped with dual lidar sensors, a spherical camera and a Trimble Applanix AP50+ GNSS-INS system.

To establish a traditional baseline, researchers utilized the IN-Fusion+ single base processing mode. The assumption was simple: a local base station located less than 5 kilometers away would yield the ultimate GNSS-INS trajectory solution for lidar georeferencing.

Ground control points (GCPs) were surveyed using a dense reference network and a Trimble terrestrial 3D laser, all referenced to the ETRS89 datum. To eliminate datum defects, the exact same base station was used for both the GCP surveys and the single base trajectory post-processing. Control was split into 33 vertical road markings and 13 horizontal checkerboard targets.

The resulting smoothed best estimate of trajectory (SBET) files from both modes were processed in Trimble Business Center (TBC) to generate independent point clouds. In both scenarios, researchers achieved 100% fixed ambiguity epochs.

Data delivers clarity

Phase 1 evaluated vertical performance across the 33 evenly distributed GCPs. Automated delta height extraction pulled data from each loop. While the single base mode held a slight advantage in the first mission, PP-RTX proved superior in missions two and three.

By the third mission, the vertical RMS error for PP-RTX dropped to a remarkable 0.8 cm. An analysis of the combined results revealed that PP-RTX and single base delivered nearly indistinguishable vertical performance. Any minor variances fell well within expected statistical noise, proving that PP-RTX delivers sub-2-centimeter vertical RMS accuracy completely base-free.

Phase 2 shifted the focus to horizontal precision using the 13 checkerboard targets. Because horizontal measurement in a point cloud requires manual survey extraction, the statistics incorporate minor operator measurement errors.

The 2D standard deviation for all missions hovered around a spectacular 1 cm for both processing modes. However, the PP-RTX horizontal RMS value was influenced by a 25 mm global-to-local datum offset, primarily in the east component. This slight shift was caused by the natural variation between the global CenterPoint® RTX service and the local ETRS89 reference station. Despite this predictable datum shift, the PP-RTX post-processing exhibited exceptional repeatability and stability across every loop.

Ditching the baseline

When evaluating total 3D performance via standard deviation, both contemporary PP-RTX and conventional single base processing kept errors under 15 mm.

The empirical results from the Biberach missions underscore the precision of the PP-RTX solution. Using standard deviation as the primary metric for consistency, the trajectory demonstrated an overall horizontal standard deviation of 1.2 cm and a vertical standard deviation of 0.8 cm.

While a 25 mm systematic shift exists due to the difference between global and local coordinate frames, the sub-1.5-centimeter standard deviation proves the trajectory’s absolute stability. Ultimately, by eliminating the logistical complexity and hardware costs of local base station deployment, PP-RTX — now included in POSPac Complete and RTX Complete — provides a highly efficient, cost-effective path to survey-grade accuracy. Tradition has officially lost its baseline.