The geodetic adjustment of a traverse network. What and why?
What is a geodetic adjustment?
Geodetic adjustment is an essential process within land surveying that is applied to correct measurement errors and improve the accuracy of geodetic measurements. It is a complex mathematical procedure used to optimize and harmonize the measurements of points in a terrain network. This process is of great importance because it helps to identify and eliminate systematic and random measurement errors, allowing reliable and accurate measurement data to be obtained for various applications, such as land surveying, cartography, geodesy, and construction and infrastructure projects. This forms the basis of almost every surveying process and is often performed at the start of works. It is frequently the first task a land surveyor must undertake.
What is its purpose?
The purpose of a geodetic adjustment can best be understood by looking at the challenges and variables that land surveyors face during measurements in the field. These include:
1. Measurement errors: Measurements are never 100% accurate due to various factors such as instrumental inaccuracy, atmospheric influences, satellite deviations, uneven terrain conditions, and human error. These measurement errors can accumulate and result in inaccurate measurements.
2. Unknown truths: In many cases, the exact location of a point on the terrain is not known, and surveyors must perform measurements relative to neighboring points, which can lead to the accumulation of errors.
The adjustment seeks to address all these issues and provides the following benefits:
1. Error identification: An adjustment makes it possible to identify measurement errors by comparing measurements and detecting deviations. This includes systematic errors (e.g., instrumental errors) and random errors (e.g., random measurement uncertainty). By always being able to start from the same network of points, these errors are detected more quickly.
2. Error compensation: The process compensates for measurement errors by calculating the best estimate of the most probable actual positions of measured points.
3. Optimization: Adjustment optimizes the measurements to ensure they are mutually consistent and meet certain mathematical criteria. The minute error, known as the misclosure, is distributed, as it were, over multiple points.
Intermezzo: What is a misclosure?
Within the context of geodetic adjustment, the concept of ‘misclosure’ plays a crucial role. Misclosure refers to the difference between the calculated values of measurements performed from different directions to a common point and the actual values of those measurements. It is a direct indicator of the degree of inaccuracy in a terrain network and is a measure of the quality of the surveying data.
Misclosures can be caused by various factors, such as measurement errors,
inaccurate instruments, atmospheric disturbances, and uneven terrain conditions. The goal of geodetic adjustment is to minimize misclosures by optimizing and harmonizing measurements so that they are as close as possible to the actual values.
The process of adjustment involves establishing mathematical models and algorithms to calculate and minimize the misclosures. The final result is a set of corrected measurements that are mutually consistent and provide a reliable picture of the geometric characteristics of the measured terrain. This enables land surveyors to produce accurate data relevant to the entire environment of the adjustment, and not just correct for the location where the measurement took place.
For example, a height can also be compared with a height on the other side of the site, given that the deviations between these zones have been compensated against each other.
To perform these operations, we use the software Move3.
In short, geodetic adjustment is a crucial step in the surveying process that corrects measurement errors, ensures the consistency of measurements, and improves the accuracy of geographic data, which is essential for numerous technical and scientific applications. Without this application, significant discrepancies will occur when the same thing is measured multiple times.
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The adjustment of a traverse network seeks to address all potential topographical problems and ensures optimization, compensation, and identification of any possible measurement deviations by evenly distributing the various measurements and their deviations across the entire “measurement network”. Through this mathematical calculation, it is possible to measure consistently with millimeter precision.