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# edgeConstraints

Package: robotics

Edge constraints in pose graph

## Syntax

``relPoses = edgeConstraints(poseGraph)``
``[relPoses,infoMatrices] = edgeConstraints(poseGraph)``
``[relPoses,infoMatrices] = edgeConstraints(poseGraph,edgeIDs)``

## Description

````relPoses = edgeConstraints(poseGraph)` lists all edge constraints in the specified pose graph as a relative pose.```
````[relPoses,infoMatrices] = edgeConstraints(poseGraph)` also returns the information matrices for each edge. The information matrix is the inverse of the covariance of the pose measurement.```
````[relPoses,infoMatrices] = edgeConstraints(poseGraph,edgeIDs)` returns edge constraints for the specified edge IDs.```

## Input Arguments

collapse all

Pose graph, specified as a `PoseGraph` or `PoseGraph3D` object.

Edge IDs, specified as a vector of positive integers.

## Output Arguments

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Relative poses measured between nodes, returned as an n-by-3 matrix or n-by-7 matrix.

For `PoseGraph` (2-D), each row is an `[x y theta]` vector, which defines the relative xy-position and orientation angle, `theta`, of a pose in the graph.

For `PoseGraph3D`, each row is an ```[x y z qw qx qy qz]``` vector, which defines the relative xyz-position and quaternion orientation, ```[qw qx qy qz]```, of a pose in the graph.

### Note

Many other sources for 3-D pose graphs, including `.g2o` formats, specify the quaternion orientation in a different order, for example, `[qx qy qz qw]`. Check the source of your pose graph data before adding nodes to your `PoseGraph3D` object.

Information matrices, specified in compact form as a n-by-6 or n-by-21 matrix, where n is the number of poses in the pose graph.

Each row is a vector that contains the elements of the upper triangle of the square information matrix. The information matrix is the inverse of the covariance of the pose and represents the uncertainty of the measurement. If the pose vector is `[x y theta]`, the covariance is a 3-by-3 matrix of pairwise covariance calculations. Typically, the uncertainty is determined by the sensor model.

For `PoseGraph` (2-D), each information matrix is a six-element vector. The default is `[1 0 0 1 0 1]`.

For `PoseGraph3D`, each information matrix is a 21-element vector. The default is ```[1 0 0 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 1 0 1]```.

## Extended Capabilities

#### Introduced in R2018a

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