If active, SNT uses the [https://en.wikipedia.org/wiki/A*_search_algorithm A* search algorithm] to automatically construct paths between two manually selected points. To manually place each node in a path, toggle this feature OFF.
A quick way to improve the quality and efficiency of the pathfinding is to enable "Hessian-based analysis", which filters the image for tube-like structures. Two parameters need to be chosen:
* '''Sigma''' - Controls the spatial scale of the filtering. A lower value of sigma will capture small structural details but is more sensitive to noise. A larger value of sigma will consider larger scale structure, but may be less sensitive to local shape characteristics. It is generally advisable to pick a value which reflects the average radius of the structures you are tracing.