What is the accuracy difference between Fixed and Float RTK?

Fixed RTK typically delivers ±8 mm horizontal and ±15 mm vertical accuracy. Float RTK carries ±300–1000 mm of positioning error depending on baseline length and atmospheric conditions.

Why does my RTK show Fixed but coordinates are still wrong?

Common causes are a datum mismatch (wrong coordinate system), an incorrect geoid model applied to elevation, or an antenna height entry error.

How do I know if multipath is affecting my survey?

Multipath typically shows as unstable repeated measurements — the same physical point measured three times gives results differing by 20–50 mm rather than the expected ±8 mm.

Can I survey during ionospheric storms?

RTK accuracy degrades during geomagnetic storms (Kp index above 5). For precision engineering or cadastral surveys, postpone sessions until the Kp index drops below 3.

What is the maximum reliable CORS baseline for centimetre accuracy?

Most CORS networks guarantee ±10–20 mm horizontal accuracy within 50 km of the nearest reference station. Beyond 70 km, deploy a self‑deployed base station within 15 km of the survey area.

APEKS FAQ | How to do point calibration?

2025-06-17

How to Calculate Transformation Parameters for Accurate GNSS Point Correction

Whether you're using a brand-new GNSS receiver or switching devices in an ongoing project, calculating transformation parameters is key to ensuring your points are correctly aligned with your control network. In this blog post, we'll guide you through the step-by-step process of localization (also called coordinate transformation) and share 3 important tips to help you avoid common calibration errors.

🛠 Step-by-Step: How to Calculate Transformation Parameters

1. Prepare Your Setup

Before starting, connect your device and create a new project. Wait until your rover gets a FIXED status — this means your GNSS signal is stable and ready to collect accurate data.

2. Add Your First Control Point

·Go to Control Point 2
·Tap Localization
·Tap Add
·Enter the known coordinates manually or select from the point library
·Tap to collect GNSS coordinates
·Tap OK

3. Add the Second Control Point

·Go to Point 1
·Tap Add
·Enter the known coordinates
·Collect GNSS coordinates again
·Tap OK

4. Calculate and Check

·Tap Calculate
·Tap OK
·You’ll see two key values:
- -Rotation – should be close to 0° or 360°
- -Scale – should be close to 1 (1.000/1.0000/0.999/0.9999)

If these values look good, tap Apply to complete your transformation.

✅ 3 Pro Tips for Accurate Point Calibration

1. Control Points Should Surround Your Site

Try to place your control points around the perimeter of your working area. Avoid putting all of them on one side — this helps ensure the transformation is balanced.

📏 Bonus Tip: Try not to go more than twice the radius of the control point area when working outside that boundary.

2. Avoid Straight-Line Placement

Don’t place your control points in a straight line — this can cause significant vertical (height) errors.

·For linear projects like roads:
- -If the project is under 6 km, place control points at both ends.
- -For longer projects (e.g., 50 km), divide it into smaller sections and localize each separately.

3. Always Check the Residuals

After calibration, review the residuals (the differences between known and calculated coordinates).

The smaller the residual, the better your transformation quality.

Final Thoughts

Calculating transformation parameters may seem technical at first, but once you understand the steps and best practices, it becomes a straightforward routine. Proper localization ensures high precision in your survey work, reduces errors, and builds trust in your data.

If you're using the APEKSURV software, this workflow can be done quickly and efficiently right from your controller.

If you found this article helpful, be sure to check out more tips, tutorials, and product details on our website.

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