# edgeResidualErrors

Compute pose graph edge residual errors

## Syntax

``resErrorVec = edgeResidualErrors(poseGraphObj)``

## Description

example

````resErrorVec = edgeResidualErrors(poseGraphObj)` returns the residual errors for each edge in the pose graph with the current pose node estimates. The residual errors order matches the order of edge IDs in `poseGraph`.```

## Examples

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Optimize a pose graph based on the nodes and edge constraints. Trim loop closed based on their edge residual errors.

Load the data set that contains a 2-D pose graph. Inspect the `poseGraph` object to view the number of nodes and loop closures.

```load grid-2d-posegraph.mat pg disp(pg)```
``` poseGraph with properties: NumNodes: 120 NumEdges: 193 NumLoopClosureEdges: 74 LoopClosureEdgeIDs: [120 121 122 123 124 125 126 127 128 129 130 ... ] LandmarkNodeIDs: [1x0 double] ```

Plot the pose graph with IDs off. Red lines indicate loop closures identified in the dataset. The poses in the graph should follow a grid pattern, but show evidence of drift over time.

```show(pg,'IDs','off'); title('Original Pose Graph')```

Optimize the pose grap using the `optimizePoseGraph` function. By default, this function uses the `"builtin-trust-region"` solver. Because the pose graph contains some bad loop closures, the resulting pose graph is actual not desirable.

```pgOptim = optimizePoseGraph(pg); figure; show(pgOptim);```

Look at the edge residual errors for the original pose graph. Large outlier error values at the end indicate bad loop closures.

```resErrorVec = edgeResidualErrors(pg); plot(resErrorVec); title('Edge Residual Errors by Edge ID')```

Certain loop closures should be trimmed from the pose graph based on their residual error. Use the `trimLoopClosures` function to trim therse bad loop closures. Set the maximum and truncation threshold for the trimmer parameters. This threshold is set based on the measurement accuracy and should be tuned for your system.

```trimParams.MaxIterations = 100; trimParams.TruncationThreshold = 25; solverOptions = poseGraphSolverOptions; ```

Use the `trimLoopClosures` function with the trimmer parameters and solver options.

`[pgNew, trimInfo, debugInfo] = trimLoopClosures(pg,trimParams,solverOptions);`

From the `trimInfo` output, plot the loop closures removed from the optimized pose graph. By plotting with the residual errors plot before, you can see the large error loop closures were removed.

```removedLCs = trimInfo.LoopClosuresToRemove; hold on plot(removedLCs,zeros(length(removedLCs)),'or') title('Edge Residual Errors and Removed Loop Closures') legend('Residual Errors', 'Removed Loop Closures') xlabel('Edge IDs') ylabel('Edge Residual Error') hold off```

Show the new pose graph with the bad loop closures trimmed.

`show(pgNew,"IDs","off");`

## Input Arguments

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Pose graph, specified as a `poseGraph` or `poseGraph3D` object.

## Output Arguments

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Edge residual errors for pose graph, specified as a vector of positive scalars.

## Version History

Introduced in R2020b