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 author, 1998. Status ------ It mostly works. Read `mj-msc-full.pdf` for visual examples and possible gotchas. ![line simplification example](https://raw.githubusercontent.com/motiejus/wm/main/salvis.png) Structure --------- There are be 2 deliverables: - `wm.sql`, the implementation. - paper `mj-msc-full.pdf`, a MSc thesis, explaining it. 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 mj-msc-full.pdf Thesis for publishing test Unit tests (fast) test-rivers Rivers tests (slow) clean Clean the current working directory clean-tables Remove tables created during unit or rivers tests help Print this help message wc Character and page count refresh-rivers Refresh rivers-*.sql from Open Street Maps ``` 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. Building the paper (pdf) ------------------------ ``` # make -j$(nproc) mj-msc-full.pdf ``` `mj-msc.tex` results in `mj-msc-full.pdf`, which will be at some point published to this repo. It needs quite a few dependencies, including a functioning Docker environment, postgresql client, geopandas, pygments, osm2pgsql, poppler, and a "quite extensive" LaTeX installation. Tested on Debian 11. Contributing ------------ This repository is frozen and will not accept contributions. Please fork it. If fork has improved the algorithm substantially, feel free 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.