81 lines
2.5 KiB
Markdown
81 lines
2.5 KiB
Markdown
Wang–Müller algorithm in PostGIS
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This is a work-in-progress implementation following "Line generalization based
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on analysis of shape characteristics" by Wang and Müller, 1998.
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Structure
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---------
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There will be 2 deliverables from this folder:
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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` is an OpenStreetMap snapshot of select 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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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. It needs quite a few dependencies, including a functioning Docker
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environment, postgresql client, geopandas, pygments, osm2pgsql, poppler, and a
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"quite extensive" LaTeX installation. This was tested on Debian 11.
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Contributing
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------------
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Please reach out to me before contributing. As of writing, this is not ready to
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accept broader contributions, TODO:
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- [x] Elimination operator.
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- [x] Exaggeration operator.
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- [ ] Combination operator.
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- [ ] CI.
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- [ ] Known bug in `wm_self_crossing`: the program crashes with a river in
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Lithuania.
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License
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-------
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GPL 2.0 or later, same as PostGIS.
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