---
title: Overlays
slug: ncam-reality/overlays
docTags: 
createdAt: 2021-09-02T02:19:47.000Z
---

## Lens Calibration Overlays

There are a number of different overlays that can be added to the lens calibration interface to aid with certain steps of calibration

To some degree their use depends on personal preference, however the "**3D Grid Optical Image Center Adjustment**" overlay is required for conducting the **center shift** part of the calibration

***

**None** - No overlay is displayed

**3D Grid Optical Image Center Adjustment** - This is used for the center shift calibration, the intersection of the white lines represents the calibrated center of the image



![](https://api.archbee.com/api/optimize/Qn0sdcVrDcDbwMFmH0oYn/uBp7h1MobinY-5EcoWOMa_overlays01.png "3D Grid Optical Image Center Adjustment")





**Last 3D Grid Position **- This overlay has been deprecated and will be removed from subsequent releases 

**Live 3D Grid Position - **Will overlay a grid pattern over a calibration chart that has been detected in the camera feed. "**Start**" has to be pressed for this to work



![](https://api.archbee.com/api/optimize/Qn0sdcVrDcDbwMFmH0oYn/r7BVj92wLbrMk3jOIB2XQ_overlays02.png "Live 3D Grid Position")



**Live Datum 3D Grid** - Displays a Grid plane aligned to the zero point (that is selected outside of lens calibration in **image modelling**)



![](https://api.archbee.com/api/optimize/Qn0sdcVrDcDbwMFmH0oYn/LBRglgcTWXtJK8AeAoJ14_overlays03.png "Live Datum 3D Grid")



**Live Datum Cube** - Displays a wireframe cube at the zero point position



![](https://api.archbee.com/api/optimize/Qn0sdcVrDcDbwMFmH0oYn/U66CzyGAyJUD69Qjh6-qw_overlays04.png "Live Datum Cube")



**Live Ncam Logo** - Displays an exact copy of the Ncam cube that is seen in the **augmented reality** tab



![](https://api.archbee.com/api/optimize/Qn0sdcVrDcDbwMFmH0oYn/feKNh4ORwy_Epu86_j-e-_overlays05.png "Live Ncam Logo")



## Using the Overlays

There are a number of techniques available when using the overlays.  The **Cube, Ncam Logo and Live Datum 3D grid** overlays can essentially all be used in the same fashion, while the use of the **Live and Last 3D grid** options differs slightly

### Cube, Ncam, Live Datum option

These overlay's are used to display where the zero point has been positioned in the world.  Typically after the first point of calibration has been done (the Golden point) the user will exit the calibration, position the zero point, then return to the calibration screen and display one of these overlays.

This allows the user to see how a CG object behaves while calibrating and makes it easy for manual adjustments to be made (to the H Focal for instance) and see them reflected on the CG without having to exit calibration

### Live 3D grid option

This option will snap a grid to a detected chart in the frame. The workflow with it is typically:

- In the lens calibration interface select the Live 3D grid overlay option
- Adjust the zoom and focus of the lens until you are at your "Golden Point"
- Position a chart in front of the camera and make sure it can not move
- Press **Start** in the **Profiler** tab
- The chart should be detected and a 3D grid overlay should be displayed over it
- Press **Stop** in the **Profiler** tab
- From this point on do not move the camera or chart at all
- Slowly zoom and focus throughout the range of your lens, the grid should stay locked onto the chart.  If it drifts away in places it indicates areas where the calibration is not correct

:::hint{type="warning"}
Of the two techniques, the Live 3D grid option is typically more prone to error and it is recommended to use the cube/Ncam/datum option.
:::

### 3D Grid Optical Image Center Adjustment

This overlay is used to adjust the center shift when working on zoom lenses.

To use it:

- Display the 3D Grid Optical Image Center Adjustment overlay
- Zoom all the way in on the lens\\
- Pan and tilt the camera until the white lines are centered on a recognizable and fixed feature in the environment (Door Frame, corner etc)
- Zoom all the way out making sure to not pan or tilt the camera at all
- If the cross hair has shifted from the feature it was positioned over, use "**Ctrl+LMB**" to drag it back to the correct position. For small adjustments use "**Ctrl+Alt+LMB**" instead

This [link](https://drive.google.com/file/d/1BoMwxFpbdo2l1fpILfKD3jl64BOXLmPC/view?usp=sharing) provides more detail on the process