93 lines
2.7 KiB
Markdown
93 lines
2.7 KiB
Markdown
Wang–Müller algorithm in PostGIS
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This is Wang–Müller line generalization algorithm implementation in PostGIS.
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Following "Line generalization based on analysis of shape characteristics" by
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the same author, 1998.
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Status
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------
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It mostly works. Read `mj-msc-full.pdf` for visual examples and possible
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gotchas.
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Structure
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---------
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There are be 2 deliverables:
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- `wm.sql`, the implementation.
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- paper `mj-msc-full.pdf`, a MSc thesis, explaining it.
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It contains a few supporting files, notably:
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- `tests.sql` synthetic unit tests.
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- `test-rivers.sql` tests with real rivers.
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- `Makefile` glues everything together.
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- `layer2img.py` converts a PostGIS layer to an embeddable image.
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- `aggregate-rivers.sql` combines multiple river objects (linestrings or
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multilinestrings) to a single one.
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- `init.sql` initializes PostGIS database for running the tests.
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- `rivers-*.sql` are national dataset snapshots of rivers (`Makefile`
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contains code to update them).
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- ... and a few more files necessary to build the paper.
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Running
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-------
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`make help` lists the select commands for humans. As of writing:
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```
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# make help
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mj-msc-full.pdf Thesis for publishing
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test Unit tests (fast)
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test-rivers Rivers tests (slow)
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clean Clean the current working directory
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clean-tables Remove tables created during unit or rivers tests
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help Print this help message
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wc Character and page count
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refresh-rivers Refresh rivers-*.sql from Open Street Maps
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```
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To execute the algorithm, run:
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- `make test` for tests with synthetic data.
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- `make test-rivers` for tests with real rivers. You may adjust the rivers and
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data source (e.g. use a different country instead of Lithuania) by changing
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the `Makefile` and the test files. Left as an exercise for the reader.
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N.B. the `make test-rivers` fails (see `test-rivers.sql`), because with higher
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`dhalfcircle` values, the unionized river (`salvis`) is going on top of itself,
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making the resulting geometry invalid.
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Building the paper (pdf)
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------------------------
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```
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# make -j$(nproc) mj-msc-full.pdf
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```
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`mj-msc.tex` results in `mj-msc-full.pdf`, which will be at some point
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published to this repo. It needs quite a few dependencies, including a
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functioning Docker environment, postgresql client, geopandas, pygments,
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osm2pgsql, poppler, and a "quite extensive" LaTeX installation. Tested on
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Debian 11.
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Contributing
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------------
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This repository is frozen and will not accept contributions. Please fork it.
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If fork has improved the algorithm substantially, feel free to ping me, I will
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link to it in this README.
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Credit
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------
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[Nacionalinė Žemės Tarnyba](http://nzt.lt/) for the river data sets.
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License
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-------
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GPLv2 or later.
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