## 3 Results
### Pilot Adjustment of Early Unified Control Points (2008-2010) for Strategy Validation
This ensured spatial continuity and significantly reduced the influence of regional boundary effects on the final coordinate estimates. Figure 7 illustrates the frequency distributions of coordinate standard deviations (1\(\sigma\)) for the north, east, and up components, based on the combined dataset over a three-year period. While the figure reveals that more than half of the horizontal deviations (N and E) exceed \(\pm\)5 mm, this is largely due to the aggregation of all years. A year-by-year analysis reveals more stable results, with a mean deviation of +0.73 mm in the north direction (\(\sigma\) = \(\pm\)4.65 mm), \(-\)1.86 mm in the east direction (\(\sigma\) = \(\pm\)3.46 mm), and a vertical RMSE of approximately 30.35 mm. The average horizontal RMSE was calculated as 6.13 mm. These findings not only indicate that residual errors exist in the year-by-year adjustments, but also highlight the spatial distortions and inconsistencies inherent to the regionally segmented adjustment strategy. In contrast, the integrated approach offers improved coordinate precision and spatial consistency, reinforcing the necessity for nationwide adoption to enhance the positional accuracy and geodetic reliability of Korea's control network. The consistent magnitude and directional patterns of the differences suggest that the primary source of the discrepancies was not the software used (i.e., GAMIT/GLOBK vs. Bernese), but also the adjustment methodology. Previous regional approaches often applied independent baseline networks and localized constraints, which introduced discontinuities across administrative boundaries and observation years. These inconsistencies accumulated over time, leading to spatial distortions in the official coordinates. In contrast, the integrated adjustment adopted in this pilot study applied a unified modeling framework, a consistent set of fixed stations, and harmonized stochastic assumptions across the entire network. As a result, the integrated adjustment yielded coherent, homogenous, and statistically robust coordinate estimates. This pilot evaluation confirms the feasibility and accuracy of the proposed nationwide adjustment strategy. The results strongly support the full-scale implementation of this approach to unify Korea's spatial reference system, improve geodetic consistency, and enhance the overall reliability of the national control point infrastructure. Figure 7: Frequency distributions of the coordinate standard deviations (1\(\sigma\)) for the north, east, and up components of the adjusted UCPs, based on the combined three-year dataset. The histograms illustrate the overall dispersion and precision of the adjusted coordinates in each directional component. In addition to the statistical summaries, spatial visualizations of coordinate differences further illustrate the effectiveness of the integrated adjustment. Figure 8 displays the horizontal vector differences between the official coordinates derived from previous KGD-based regional adjustments and the results from the integrated adjustment of UCPs installed from 2008 to 2010. The arrows represent both direction and magnitude of positional discrepancies. Clear regional patterns are observed, particularly in areas where independent local adjustments were previously applied, suggesting the accumulation of distortions due to inconsistently defined baselines and constraints. Figure 9 presents the vertical component of the coordinate differences between the two adjustment strategies. The map reveals substantial variation in ellipsoidal height values, with differences exceeding several decimeters in certain regions. These inconsistencies are primarily attributed to GNSS vertical sensitivity and the absence of leveling-based height control in earlier local adjustments. Figure 8: Horizontal coordinate differences between previous KGD-based regional adjustments and the integrated adjustment of UCPs from 2008 to 2010.