APClean is a Windows program that can be used to quickly remove wrong control points from a PTGui project file.

Autopano is a very useful program because it can automatically find a lot of control points, but sometimes it finds some wrong control point too. You can run the optimizer and look for control points with a very high distance, but this is a slow solution. APClean can remove the control points with a distance higher than normal in a quick and simple way.

APClean works on an image pair basis: it analyzes each image pair and it finds control points with an higher than normal distance for that image pair. The analysis is not done at a global level, but at an image pair level: this means that if an image pair has much higher distances than the others its control points will not be removed more quickly than the others.

For each image pair APClean computes the mean value of the control point distances and their standard deviation (it is a measure of how much the distances are scattered: a higher standard deviation means that the distances are very different, a smaller value means that the distances are very similar). These values are used to compute the threshold value for that image pair: if a control point distance is greater than the threshold it will be removed. The threshold is computed as mean + n*std_dev, where n is a value chosen by the user. This formula makes sure that only distances significantly greater than the others in that image pair will be removed.

It is possible to remove all the control points for an image pair: this can be useful if Autopano has linked two images that should not be linked. For example, if there is a lot of overlap, it could link image 1 with image 2 and image 3. Removing the control points between image 1 and image 3 will help the optimizer.

How to use APClean

It is better to use APClean immediately after using Autopano in PTGui, before manually adding control points. Just run the optimizer in order to compute the control points distances, save the project and run APClean.

One or more wrong control points can cause higher distances for right control points too, so it is better to start removing only a few control points that have really high errors. Then you can run PTGui to optimize the project again: having removed some wrong control point will change the distance of other control points too, giving a more correct result.

You can remove some control point and optimize the project again until you have only correct control points. APClean will not lose the project file name so do not need to select it again: just press the Read project button again.


Click here to download APClean (212 Kb). The program does not need to be installed: just unzip all the files in a folder and run APClean.exe.

APClean in a .NET program, so it needs the Microsoft .NET Framework V1.1. The framework is conceptually similar to the Java virtual machine: you need to install it once, then you will be able to run every program that uses it. You may wonder if the framework is installed in your computer: you can look at the installed programs in your control panel, or you can simply try and run APClean. If the framework is not installed you will get an error message.

Microsoft recommends that you install the Framework using Windows Update. When you start Windows Update it opens the Important Updates and Service Packs page but you cannot download the Framework from there. Select Windows XP (or Windows 2000) from the left pane and then you will be able to download the .NET Framework. This is a good solution if you have a fast internet connection, since the download size is about 23Mb.