Topographic Representation in Trimble Business Center

PUBLICATION 01 | TBC CYCLE | GEOCOM Engineering

 

Introduction

A topographic representation corresponds to a model of reality created from a variety of techniques which, given today's precision and productivity requirements, need to be conveniently combined in an integrated calculation and drawing process, ensuring the absolute reliability of the final product.

Accordingly, Trimble Business Center (TBC henceforth) offers a series of advantages when it comes to managing the calculation of data from geometric leveling, total station, GNSS, laser scanner, drones (photographs and LiDAR), and point clouds. TBC allows for a convenient combination of geospatial observation techniques with the aim of delivering results obtained under a single platform, optimizing the office workflow.


GNSS and Optics

TBC processes data from GNSS receivers in any of their modalities (static, PPK, RTK, and RTX) and from optical devices such as total stations and digital levels. The data produced by these instruments are vital in terms of making observations that are fundamental for the densification of extremely high-precision geodetic positions within the context of a network, which is the elemental basis required for any topographic representation.

For its part, GNSS enables the georeferencing of topographic surveys through the densification of the National Geodetic Network, which is linked to SIRGAS in a variety of epochs. This operation is usually performed by statically observing a determined set of GNSS baselines that ultimately form a network, which requires an adjustment of its observations for the determination of precise coordinates.

In addition, TBC features Trimble RTX to process the same static observations, allowing for the calculation of geodetic positions referred to SIRGAS without the need to process baselines referred to a reference station. Finally, TBC also manages RTK data, which applies to scenarios related to conventional topographic representation, allowing for recalculation or, directly, moving to the drawing stage.

 

Figure 1. GNSS network adjustment in TBC


On the other hand, optical geodetic observation technologies have gained a space that is absolutely associated with tasks requiring extremely high precision. For example, total stations with automatic aiming systems, such as Autolock or Finelock, have set a standard in underground works that demand precise geodetic control with the highest possible productivity. In this same vein, geometric leveling allows for connection to the physical height system, densifying the vertical component with a precision only associated with this technique. Both types of observations are supported by TBC in terms of calculation with full reportability.

 

Figure 2. Terrestrial network adjustment (total station observations) in TBC

 

Drones and Photogrammetry

Just as the technology associated with GNSS and optics is directly linked to the establishment of geodetic control networks, drones have provided a way to represent reality in an extremely efficient manner, using the foundation provided by GNSS and optical technology, delivering highly representative results. Drones have changed the way topographic representations are made, offering a level of productivity never before seen in the industry.


Figure 3. Visualization of orthophoto produced in TBC

Thus, drones gave a new meaning to photogrammetry, making it an easily implemented technique for jobs requiring extensive topographic representations. However, a large computational processing capacity is required, coupled with the difficulty of managing a vast volume of data when creating the topographic representation. TBC solves this by incorporating an aerial photogrammetry module capable of processing photographs from any drone, either by processing GNSS trajectories to calculate the precise position of each photograph or by using control points to refer the aerotriangulation to a defined reference frame. In addition, the final products of photogrammetry (orthophotos and point clouds) can be combined with other geospatial data with the aim of centralizing the entire calculation and drawing operation.

 

Point Clouds and Images

Not only aerial photogrammetry produces point clouds. Laser scanners, in their different types (terrestrial, aerial or SLAM) produce point clouds along with capturing images. In this context, during the data capture process, laser scanners do not have the ability to discriminate what is relevant to produce the topographic representation. For this reason, in the calculation and drawing stage, a data filtering and sampling strategy needs to be incorporated.

Thus, point cloud classification is absolutely necessary. Typically, especially for point clouds created with aerial photogrammetry, the goal is to isolate the terrain from other classes, which is known as terrain classification. TBC not only classifies the terrain from a point cloud, but also other default classes. If a class is not included, TBC has the ability to train an algorithm to classify a new feature through the use of Deep Learning. There is also a tool to smooth the point cloud through grid-based sampling where each cell produces a point resulting from an operation (average, maximum, or minimum) using the points contained within it. Finally, a point cloud will be ready to produce a topographic representation.

 

Figure 4. Classified and sampled point cloud in TBC

 

In addition to the point cloud, captured images help color it, proving useful for producing data that is qualitatively interpretable. Images can also contribute to documenting temporal effects in the understanding that it is something not identifiable by the quantitative component.

 

Topographic Representation and Final Deliverables

Once all operations aimed at controlling the quality of geospatial data, along with creating entities that are representative for the intended purposes, have been completed, the stage begins to produce the geometries required for modeling reality to create the final deliverable.

In this context, TBC presents a CAD from which 2D and 3D polylines can be drawn from topographic data along with the creation of surfaces for a detailed representation. In addition, using surfaces as a basic input, profiles can be traced through the creation of alignments and corridors. In this same vein, point clouds provide the basis for the automatic creation of lines. For example, if a curb is represented through a point cloud, TBC allows for the automatic extraction of breaklines that simplify the modeling of this element. For their part, orthophotos, produced from photographs, can be used to quickly identify 2D elements.

 

Figure 5. Surfaces in TBC

 

Finally, conventional topographic data, orthophotos, and point clouds converge for the automatic creation of sheets that can be viewed in CAD or PDF, which are openly shared for data analysis.

 

Practical Experience

For more details on the different functionalities of TBC, don't miss the cycle of publications that will thoroughly showcase, based on a real-world experience combining GNSS and aerial photogrammetry, the various functionalities of TBC for producing topographic representations.

 

Figure 6. Final product created in Trimble Business Center