Tech Chat | Grid to Ground: Bridging the Gap Between RTK & Total Station Observation

2023-12-13

In precision measurement projects, the seamless integration of total stations and GNSS equipment is essential. Surveyors often find themselves balancing the use of total stations for accuracy in heavily obscured satellite signal areas and GNSS equipment for swift and precise measurements in open spaces. However, the combination between these two systems can introduce errors in the form of inconsistent grid coordinates from GNSS and ground coordinates from the total station.

Understanding the Discrepancy: Grid vs. Ground Coordinates

The discrepancy arises due to the calculation process introducing projection deformation in the grid coordinates measured by GNSS-RTK. On the other hand, total stations provide distances between ground coordinates, prompting the need to convert grid coordinates to ground coordinates to identify closure errors.

Defining Ground and Grid Coordinates

Ground coordinates represent distances on the actual earth's surface, considering the ellipsoidal shape and the impact of elevation. On the other hand, grid coordinates are part of coordinate systems involving projections and datums, where the projection method determines how ground positions are projected onto a map or grid.

Conversion Process in SingularPad Software

In the SingularPad software, the conversion of grid to ground coordinates involves the Combined Scale Factor, further decomposed into Elevation Scale Factor and Grid Scale Factor. The calculation formula is:

Combined Scale Factor = Elevation Scale Factor x Grid Scale Factor
Grid Distance = Ground Distance x Combined Scale Factor

Understanding Grid Scale Factor

Grid Scale Factor corrects projection deformation, which is influenced by the curvature of the earth and varies based on the chosen projection method and location. For example, the UTM projection has a deformation length ratio of 0.9996, with Transverse Mercator projection showing minimal deformation on the central meridian.

Exploring Elevation Scale Factor

Elevation Scale Factor corrects deformation caused by differences in height between the measurement area's ground surface and the projection plane. Assuming the projection plane is at the ellipsoid's height of 0, the deformation is linked to the elevation of the measurement area's ground surface.

Efficient Operation in SingularPad

SingularPad streamlines this conversion process by automatically calculating the Combined Scale Factor from any point. With a simple click to apply, the calculated factor is then applied to all points in the database. This ensures consistency and accuracy throughout the measurement dataset.

Conclusion

For surveying and construction projects, the combination of total stations and GNSS RTK is a trend. Understanding and addressing the differences between grid and ground coordinates through sophisticated software solutions like SingularPad ensures that surveyors can achieve accurate and reliable results in their high-precision surveying projects.

Learn more about SingularXYZ RTK and total station,

https://www.singularxyz.com/X1.html
https://www.singularxyz.com/TS1000.html
https://www.singularxyz.com/SingularPad.html