> For the complete documentation index, see [llms.txt](https://support.senterasensors.com/home/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://support.senterasensors.com/home/rtk-ppk-module/getting-started/education/relative-vs-global-accuracy.md).

# Relative vs Global Accuracy

## Global Accuracy

* Refers to how well the reconstructed model aligns with real-world coordinates (latitude, longitude, elevation).
* Critical for survey-grade mapping, GIS integration, and legal documentation.
* Achieved using:
  * Ground Control Points (GCPs)
  * RTK/PPK GNSS corrections
* Without GCPs or GNSS corrections, global accuracy can be off by meters. 

## Relative Accuracy

* Measures how accurately features are positioned relative to each other within the model.
* Important for distance, area, and volume measurements (e.g., stockpiles, building dimensions).
* Can be high even without GCPs, especially with good image overlap and low GSD (Ground Sampling Distance).
* Doesn’t guarantee correct placement on Earth’s surface. 

## Comparison

| Feature          | Global Accuracy                 | Relative Accuracy          |
| ---------------- | ------------------------------- | -------------------------- |
| Reference System | Earth based coordinates         | Internal model consistency |
| Use Cases        | Surveying, GIS, legal documnets | Measurements, inspections  |
| Key Tools        | GCPs, RTK/PPK GNSS              |                            |
| Accuracy Range   | 1 - 3cm                         | 2 - 6cm (within the model) |


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