# SAL3D > METRIC CALIBRATION TOOL

The AQSENSE SAL3D Metric Calibration Tool provides a straightforward procedure for obtaining true XYZ metric coordinates from 2.5D RangeMaps, permitting the reconstruction of the COP with metric units and removing perspective distortion. Find here how to get Range Maps for Metric

Non calibrated COP

Calibrated COP with Metric Tool

- Easy to use (see brochure for three easy steps)
- Accurate conversion 2.5Dâ†’ 3D
- Removes perspective distortion
- Linear and Static calibration

## Linear Metric Calibration

This approach involves the acquisition of the RangeMap of a specially designed object

Scanning of the Linear Metric calibration Pattern

- Accurate In-line measurement for parts with a constant linear movement (conveyors with encoder)
- Calibration pattern and object dimensions should be similar.
- The object, or the block camera-laser must have a linear displacement.

## Static Metric Calibration

This approach only requires a single profile to determine the relation between camera pixels and metric units

- A cost effective option when linear displacement is constant.
- Suited for environments where movement conditions are irregular (vibrations).
- Suited for calibration in set-ups where movement is not linear (e.g. rotating, robot arm)

To better understand the advantages and disadvantages of the Static and the Linear Calibration refer to the Static Metric Calibration Vs. Linear Metric Calibration page

## Remove Perspective Distortion

For a human observer, closer objects seem to be bigger than the same objects in a farther position (related to the observer). The observer has the impression that a long pipe, as looked at from one of its extremes, seems to be decreasing in diameter as the observer looks farther along the pipe.

This is known as Perspective Effect (see following figure) or in terms of 3D acquisition, Perspective Distortion.

The following pictures show an example of the reconstruction of a tilted cylinder using proportional reconstruction and using SAL3D Metric reconstruction. The proportional reconstruction assumes a constant ratio between pixels and metric units, but, due to perspective distortion, this assumption is not true.

Proportional cylinder reconstruction. a) Range Map; b) COP; c) ZMap

SAL3D Metric cylinder reconstruction. a) Range Map; b) COP; c) ZMap

Observing the cloud of points and also the ZMap obtained in both situations, it is clear that the proportional reconstruction distorts the object, while the SAL3D Metric reconstruction preserves the original shape.

More information at Metric Calibration Tool's documentation page (Opens in new window)