What is PPA :

An important feature of PPA is that it takes a global approach, as opposed to the local neighborhood operators used in many other algorithms. Each segment detected by PPA considers not only relations with contiguous neighboring grid points, but also strives to preserve the continuity of the global trend. This is an attempt to simulate human operators, who always factor in the overall trend of the lineament before delineating its local parts. PPA starts by connecting all points in a neighborhood that can possibly lie on the ridge axis, thus forming a belt of polygons in the first step. Next, a polygon breaking process eliminates unwanted segments according to the assumption that a ridge segment cannot be the side of any closed polygon, and that the result should be a
purely dendritic line pattern. Finally, a branch-reduction process is executed to eliminate all parallel false ridges that remained due to the conservative approach taken in the first step. Results indicate that PPA is reasonably successful in picking out ridges that would have been identified manually by experts.

Publications

2007

@article{Chang:2007:PPA,
	author  = {Yet-Chung Chang and Gaurav Sinha},
	title   = {A visual basic program for ridge axis picking on DEM data 
	           using the profile-recognition and polygon-breaking algorithm},
	journal = {Comput. Geosci.},
	year    = {2007},
	volume  = {33},
	number  = {2},
	pages   = {229--237},
}

@inproceedings{Chang:2002:PPA,
	author  = {Yet-Chung Chang and Alessandro Frigeri},
	title   = {Implementing the automatic extraction of ridge and valley axes 
	           using the PPA algorithm in Grass GIS},
	booktitle={Proceedings of the Open source GIS - GRASS users conference 2002},
	month   = {September},
	year    = {2002}
}

@article{Chang:2002:PPA,
	author  = {Yet-Chung Chang and Gwo-Shyh Song and Shu-Kun Hsu},
	title   = {Automatic extraction of ridge and valley axes using the
	           profile recognition and polygon-breaking algorithm},
	journal = {Comput. Geosci.},
	volume  = {24},
	number  = {1},
	year    = {1998},
	pages   = {83--93}
}

Software Download

PPA ridge/valley picker as a World Machine Pro Beta 5 Plug-in device
Howard Zhou