---
title: "Checking Control Point Errors after Processing"
slug: "checking-control-point-errors-after-processing-1"
tags: ["Troubleshooting"]
updated: 2026-03-06T14:27:00Z
published: 2026-03-06T14:27:00Z
---

> ## Documentation Index
> Fetch the complete documentation index at: https://knowledge.navvis.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Checking Control Point Errors after Processing

Post-processing creates error logs and graphs that show drift errors in the device trajectory before and after applying surveyed control points.

In each dataset folder under datasets_proc, two main log files are generated:

- anchors_alignment.log: control point errors before processing
- anchors.log: remaining control point errors after processing

Residual error graphs (residuals.png in the alignment/optimization folders) visualize these errors before and after post-processing, demonstrating how control points reduce trajectory drift.

## Review Control Point Error logs

Post-processing generates Error Log files that indicate drift errors in the device's trajectory before and after processing with surveyed control points.

An [introduction](/v1/docs/an-introduction-to-control-points) of drift errors and how control points are effective on reducing the errors.

Error Logs can be found in each dataset folder under *datasets_proc*, for example:

```plaintext
/datasets_proc/2024-08-24_14.16.03/anchors/
```

There exist two important files indicating the control point errors:

## anchors_alignment.log

This file reflects the control point error **before**the processing. It is created by matching the recorded control points from NavVis devices with the surveyed control point values.

A sample *anchors_alignment.log*:

```plaintext
1714466412.981071803	"6"   -0.10635   -0.01164   +0.00129   +0.00000 false true true true
1714466628.554513557	"7"   +0.00741   -0.00850   -0.00619   +0.00000 false true true true
1714466808.296838821	"8"   +0.00819   -0.02187   +0.00977   +0.00000 false true true true
1714467051.500836058	"9"   +0.01973   -0.05764   -0.00918   +0.00000 false true true true
1714467486.676680874	"1"   +0.07102   +0.09964   +0.00431   +0.00000 false true true true
```

Each line logs the following information:

- The time when the device was placed on the control point ([Unix time](https://en.wikipedia.org/wiki/Unix_time)).
- The control point's unique identifier (ID).
- The remaining position error (x, y, z).
- The orientation error (yaw; can be ignored).
- The flags (true/false) for the control point optimization stages are also displayed but can be ignored by normal users.

### anchors.log

This file reflects the remaining control point errors **after**processing. It is created by the recorded control points from NavVis devices with the surveyed control point values.

A sample *anchors.log*:

```plaintext
1714466412.981071803	"6"   +0.00015   +0.00062   -0.00001   +0.00000 false true true true
1714466628.554513557	"7"   +0.00015   -0.00014   -0.00002   +0.00000 false true true true
1714466808.296838821	"8"   +0.00001   +0.00030   -0.00026   +0.00000 false true true true
1714467051.500836058	"9"   -0.00004   -0.00040   -0.00021   +0.00000 false true true true
1714467486.676680874	"1"   -0.00043   +0.00000   +0.00019   +0.00000 false true true true
```

The file format is the same as the *anchors_alignment.log*’s above.

We can see that control point errors are better optimized after being processed by our software.

## Review Control Point Error Graphs

Another way to analyze control point errors visually is to check the residuals graph. These are visual representations of the values from the above control point errors.

The control point error graphs are generated under *datasets_proc*, for example under this path:

```plaintext
/datasets_proc/2024-08-24_14.16.03/internal/anchors/alignment
or
/datasets_proc/2024-08-24_14.16.03/internal/anchors/optimization
```

### alignment/residuals.png

The residuals.png in the alignment folder shows the errors for each control point **before**post-processing.

![](https://cdn.document360.io/bf174766-fa1a-4fe1-a4d7-b1db1e7cb996/Images/Documentation/image(41).png)

### optimization/residuals.png

The residuals.png in the alignment folder shows the errors for each control point **after**post-processing.

![](https://cdn.document360.io/bf174766-fa1a-4fe1-a4d7-b1db1e7cb996/Images/Documentation/image(42).png)

> **Note**: the scale of the graph is auto-adjusted. By comparing both residual graphs, we can see that the control points have been optimized after post-processing.