Wang–Müller line generalization algorithm in PostGIS ---------------------------------------------------- This is Wang–Müller line generalization algorithm implementation in PostGIS. Following "Line generalization based on analysis of shape characteristics" by the same authors, 1998. ![line simplification example](https://raw.githubusercontent.com/motiejus/wm/main/salvis.png) Status & Structure ------------------ There are 2 main pieces: - `wm.sql`, the implementation. - MSc thesis `mj-msc-full.pdf` with visual examples and known issues. It contains a few supporting files, notably: - `tests.sql` synthetic unit tests. - `test-rivers.sql` tests with real rivers. - `Makefile` glues everything together. - `layer2img.py` converts a PostGIS layer to an embeddable image. - `aggregate-rivers.sql` combines multiple river objects (linestrings or multilinestrings) to a single one. - `init.sql` initializes PostGIS database for running the tests. - `rivers-*.sql` are national dataset snapshots of rivers (`Makefile` contains code to update them). - ... and a few more files necessary to build the paper. Running ------- `make help` lists the select commands for humans. As of writing: ``` # make help clean Clean the current working directory clean-tables Remove tables created during unit or rivers tests help Print this help message mj-msc-full.pdf Thesis for publishing mj-msc-gray.pdf Gray version, to inspect monochrome output refresh-rivers Refresh river data from national datasets test-rivers Rivers tests (slow) test Unit tests (fast) ``` To execute the algorithm, run: - `make test` for tests with synthetic data. - `make test-rivers` for tests with real rivers. You may adjust the rivers and data source (e.g. use a different country instead of Lithuania) by changing the `Makefile` and the test files. Left as an exercise for the reader. N.B. the `make test-rivers` fails (see `test-rivers.sql`), because with higher `dhalfcircle` values, the unionized river (`salvis`) is going on top of itself, making the resulting geometry invalid during the process. Building the paper (pdf) ------------------------ ``` # make -j mj-msc-full.pdf ``` `mj-msc.tex` results in `mj-msc-full.pdf`. This step needs quite a few or a container: see `Dockerfile` for dependencies or `in-container` to run it all in the container. Contributing ------------ This repository does not accept contributoins. Please fork it. If a fork has improved the algorithm substantially, you are welcome to ping me, I will link to it in this README. Credit ------ [Nacionalinė Žemės Tarnyba](http://nzt.lt/) for the river data sets. License ------- GPLv2 or later.