# prepr [](https://gitlab.com/dickoa/prepr/pipelines) [](https://ci.appveyor.com/project/dickoa/prepr) [](https://codecov.io/gl/dickoa/prepr) [](http://www.r-pkg.org/pkg/prepr) An R package to repair broken GIS polygons using the [`prepair`](https://github.com/tudelft3d/prepair) C++ library. ## Installation The `prepair` C++ library need these two libraries to compile: - [`CGAL`](https://www.cgal.org/) - [`GDAL`](https://gdal.org/) The R package `prepr` solves the CGAL dependencies by shipping with a subset of the CGAL header. We also use [`rwinlib`](https://github.com/rwinlib) to provide `GDAL` on Windows in order to build this package from source. You will need the latest version of [`rtools`](https://cran.r-project.org/bin/windows/Rtools/) in order to build the source code on Windows. `prepair` can also use these optional libraries: - [`GMP`](https://gmplib.org/) - [`MPFR`](https://www.mpfr.org/) They are disabled by default on Windows but required if you want to build the package in a Linux/OS X environment. After installing all these libraries, you can now install the development version of the `prepr` R package from [Gitlab](https://gitlab.com/dickoa/prepr) using the `remotes` R package with: ``` r # install.packages("remotes") remotes::install_gitlab("dickoa/prepr") remotes::install_github("dickoa/prepr") ## mirror ``` ## A quick tutorial This is a simple tutorial which shows you how to solve common problems we can find with polygons: ### A ‘bowtie’ polygon: ``` r library(prepr) library(sf) p1 <- st_as_sfc("POLYGON((0 0, 0 10, 10 0, 10 10, 0 0))") st_is_valid(p1, reason = TRUE) #> [1] "Self-intersection[5 5]" p11 <- st_prepair(p1) st_is_valid(p11) #> [1] TRUE st_as_text(p11) #> [1] "MULTIPOLYGON (((0 0, 5 5, 0 10, 0 0)), ((5 5, 10 0, 10 10, 5 5)))" par(mfrow = c(1, 2)) plot(p1, main = "RAW", col = "#D7722C") plot(p11, main = "Repaired", col = "#D7722C") ``` ### Square with wrong orientation: ``` r p2 <- st_as_sfc("POLYGON((0 0, 0 10, 10 10, 10 0, 0 0))") st_is_valid(p2, reason = TRUE) #> [1] "Valid Geometry" plot(p2, main = "RAW", col = "#D7722C") ``` ### Inner ring with one edge sharing part of an edge of the outer ring: ``` r p3 <- st_as_sfc("POLYGON((0 0, 10 0, 10 10, 0 10, 0 0),(5 2, 5 7, 10 7, 10 2, 5 2))") st_is_valid(p3, reason = TRUE) #> [1] "Self-intersection[10 2]" p33 <- st_prepair(p3) st_is_valid(p33) #> [1] TRUE st_as_text(p33) #> [1] "POLYGON ((0 0, 10 0, 10 2, 5 2, 5 7, 10 7, 10 10, 0 10, 0 0))" par(mfrow = c(1, 2)) plot(p3, main = "RAW", col = "#D7722C") plot(p33, main = "Repaired", col = "#D7722C") ``` ### Dangling edge: ``` r p4 <- st_as_sfc("POLYGON((0 0, 10 0, 15 5, 10 0, 10 10, 0 10, 0 0))") st_is_valid(p4, reason = TRUE) #> [1] "Self-intersection[15 5]" p44 <- st_prepair(p4) st_is_valid(p44) #> [1] TRUE st_as_text(p44) #> [1] "POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))" par(mfrow = c(1, 2)) plot(p4, main = "RAW", col = "#D7722C") plot(p44, main = "Repaired", col = "#D7722C") ``` ### Two adjacent inner rings: ``` r p6 <- st_as_sfc("POLYGON((0 0, 10 0, 10 10, 0 10, 0 0), (1 1, 1 8, 3 8, 3 1, 1 1), (3 1, 3 8, 5 8, 5 1, 3 1))") st_is_valid(p6, reason = TRUE) #> [1] "Self-intersection[3 8]" p66 <- st_prepair(p6) st_is_valid(p66) #> [1] TRUE st_as_text(p66) #> [1] "POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0), (1 1, 1 8, 3 8, 5 8, 5 1, 3 1, 1 1))" par(mfrow = c(1, 2)) plot(p6, main = "RAW", col = "#D7722C") plot(p66, main = "Repaired", col = "#D7722C") ``` ### Polygon with an inner ring inside another inner ring: ``` r p7 <- st_as_sfc("POLYGON((0 0, 10 0, 10 10, 0 10, 0 0), (2 8, 5 8, 5 2, 2 2, 2 8), (3 3, 4 3, 3 4, 3 3))") st_is_valid(p7, reason = TRUE) #> [1] "Holes are nested[3 3]" p77 <- st_prepair(p7) st_is_valid(p77) #> [1] TRUE st_as_text(p77) #> [1] "MULTIPOLYGON (((0 0, 10 0, 10 10, 0 10, 0 0), (2 2, 2 8, 5 8, 5 2, 2 2)), ((3 3, 4 3, 3 4, 3 3)))" par(mfrow = c(1, 2)) plot(p7, main = "RAW", col = "#D7722C") plot(p77, main = "Repaired", col = "#D7722C") ``` ## Details and how to cite Details of how we automatically repair broken polygons, and what results you can expect, are available in this scientific article by the original authors of `prepair`: > Ledoux, H., Arroyo Ohori, K., and Meijers, M. (2014). A > triangulation-based approach to automatically repair GIS polygons. > *Computers & Geosciences* 66:121–131. > [\[DOI\]](http://dx.doi.org/10.1016/j.cageo.2014.01.009) > [\[PDF\]](http://3dgeoinfo.bk.tudelft.nl/hledoux/pdfs/14_cgeo_prepair.pdf) If you use the R package `prepr` for a scientific project, please cite their original work. ## License This package is released under the GPL-3 license.