Topographic Representation from GNSS-RTK

PUBLICATION 03 | TBC CYCLE | GEOCOM Engineering

 

Introduction

GNSS RTK is an excellent technique for performing topographic surveys from a discrete geospatial data acquisition perspective. GNSS RTK determines the coordinates of a variety of points with an accuracy that is compatible with different surveying applications, granting high productivity and efficiency in a variety of environments. For its part, Trimble has developed several generations of RTK processing engines, thus establishing itself as a manufacturer with extensive experience in this area. Currently, Trimble ProPoint is the latest RTK processing engine, allowing users to work in situations where GNSS previously could not.

Furthermore, Trimble Business Center (TBC) is responsible for processing GNSS RTK data through a variety of possibilities. From recalculating GNSS RTK surveys by modifying the coordinates of the origin point, to filtering RTK baselines in terms of their accuracy, and finally, producing topographic representations that can be shared in a variety of formats.


Topographic Survey: JOB format

Trimble Access is the field software for Trimble GNSS and total stations. The advantage of working with Trimble Access is basically the simplicity it offers in operation. Whether working with GNSS, total station, or a combination through Integrated Surveying, Trimble Access has a variety of applications to solve problems in the field. Additionally, Trimble Access has a direct association with TBC through the well-known JOB format.

For its part, the JOB format acts as a direct link between Trimble Access and TBC. This not only stores data related to instrument observation. In other words, the JOB format is a kind of log of what happened in the field. Furthermore, it is a format that does not allow editing of elements that must guarantee reliability.

 

Feature Library: FXL format

The topographic coding of a point corresponds to the identification of the surveyed element, which describes its characteristic. However, the definition of this point in graphic terms is interesting, as it indicates whether this code will generate a line, point, polygon, or circle. The code can also have an associated symbology type incorporated, for example, tree, pole, or in the case of polygons or lines, a line type or other element that needs to be associated with the code. It can also have a control code incorporated, which will give an instruction in terms of performing the topographic drawing (for example, at the end of a union sequence). All of the above is arranged in what is called a feature library, which is a set of topographic codes (features) that have rules for convenient drawing.

The feature library format is FXL. This library can be created in Trimble Access in a basic way and in an advanced way in Trimble's Feature Definition Manager application.

 


Figure 1. Trimble Access field software and the feature library application


The use of a feature library significantly increases productivity in the field. Instead of manually entering codes, the operator can select pre-configured buttons, even with combinations of codes that allow representing multiple features with a single point.

 


Figure 2. Trimble Access with applied feature library


To bring this survey to a final product, such as a topographic plan, it is not necessary to export the data; only the JOB needs to be extracted from the controller. By loading the JOB into TBC, it is possible to review the surveyed information and edit any data entered in the field, such as origin point coordinates, codes, instrument and rod heights, for example. Editing the base coordinate allows recalculating the entire survey, without affecting the application of the feature library. This allows obtaining a fast and accurate product during the drawing process. Therefore, as a geospatial data capture method, it is possible to set a navigation coordinate at the base, and use the RTK and Record survey style configuration if the definitive coordinates of the survey's origin point are not available, which allows performing even a photogrammetric survey with a drone in PPK mode if required. The process of calculating the coordinates of the survey's base point is described in the publication Geodetic Densification from GNSS Data.

 

Drawing in TBC

TBC, in its Drafting module, includes dimensioning, labeling, creation of surface tables, coordinate tables, importing and inserting blocks, line types, sheet configuration, dynamic views, creation of grids, among many other options.

Once the JOB is imported, reviewing and editing some parameters is simple, such as the coordinate system, geoid model, instrument heights, etc.

 


Figure 3. List of vectors from importing a JOB into TBC

 

These configurations can be saved as templates for later use in projects with similar characteristics. Templates can contain all configurations, both for GNSS and terrestrial network adjustments, text styles, formats, etc. These templates are exported in VCT format, which can be shared with the work team and stored at the following address on your computer: C:\Users\USER-PC\AppData\Roaming\Trimble\Trimble Business Center\42.0

 


Figure 4. Templates in TBC

 

TBC, with its advanced automated drawing tools, allows the creation of high-quality graphic products, including views, coordinate grids, profiles, etc., which can then be exported in CAD format.

When applying the feature library created in FXL format to the survey, the survey will be drawn according to how the points were measured in the field. If the library includes blocks, layers, and colors, these will be applied according to that configuration.

 


Figure 5. Survey display from importing a JOB into TBC in Plan View

 


Figure 6. Feature code processing

 

Once the codes are processed, the graphic elements allow further graphic operations, such as creating a surface. By incorporating these graphic elements as breaklines to create trends in the surface, the drawing process is further optimized.

 


Figure 7. Terrain surface in TBC

 

TBC has essential tools for the drawing process, such as editing triangulation by deleting triangles, exchanging directions, creating boundaries, creating islands, combining surfaces, adding graphic members, and creating contour lines, to name a few.

Once the graphic base is created, it is possible to use configured automated drawing tools, such as corridors for obtaining longitudinal and transverse profiles and incorporating them into a plan and profile template. TBC also has, as a complement to the above, the tool to create quick CAD profiles and incorporate them into the sheet in question.

This configuration allows creating a dynamic view with an incorporated grid and north arrow, orienting itself according to the created alignment, which automatically creates a UCS along its path. If the alignment is extensive, it will create the necessary sheets according to the scale configuration, so texts will adapt automatically, making it unnecessary to calculate the size.

 

Figure 8. Topographic plan configuration in TBC

 

Once this operation is performed, it is possible to create the sheets with all their CAD entities. At this stage, it is possible to make the adjustments and modifications typical of a CAD plan and then export or plot it from TBC.

 

Conclusions

The field capture workflow using Trimble Access allows for more fluid and productive surveys, reducing uncertainty when graphically representing natural and artificial features and existing works. The feature library is a fundamental tool when performing work, as it considerably helps reduce processing time in the office.

The feature library can grow and improve as work progresses, as it can be fed in the field to incorporate new features and subsequently be optimized through Feature Definition Manager.

TBC, for its part, is an integrating software for different capture techniques in a georeferenced environment, allowing the processing of GNSS and Terrestrial information simultaneously. The recalculation of data gains importance when defining the origin, and TBC fulfills this objective, ensuring unparalleled quality standards. Its drawing tools are indispensable for achieving an aesthetic and precise graphic representation, adding an artistic touch to the product, which can be used in engineering and construction tasks, project reporting, cadastral and quantification work, among other applications.

 

Figure 9. Topographic plan in TBC