[Tile-serving] [osm2pgsql-dev/osm2pgsql] Chunky rivers when generalizing water areas (Issue #2087)

[Paul Norman]

## What version of osm2pgsql are you using?

1.9.2-29-g374eca48

## What did you do exactly?

I am generalizing water tables with themepark and osm2pgsql-gen

```lua
osm2pgsql.run_gen('raster-union', {
    schema = themepark.options.schema,
    name = 'water_z12',
    dest_table = 'water_z12',
    src_table = 'water',
    zoom = level
})
osm2pgsql.run_gen('raster-union', {
    schema = themepark.options.schema,
    name = 'water_z8',
    dest_table = 'water_z8',
    src_table = 'water',
    zoom = level
})
```

## What did you expect to happen?

I expected generalized tables that would be useful at z8 and z12.

## What did happen instead?

At z8, the water areas are "chunky" when using the z8 table
![image](https://github.com/osm2pgsql-dev/osm2pgsql/assets/1190866/cb40bc77-17f5-4782-9472-3cac31203ce5)

This is rendered at 1 z8 tile = 512 device independent pixels

It's not really any better at z7
![image](https://github.com/osm2pgsql-dev/osm2pgsql/assets/1190866/83b31a28-f4d8-41dc-91f6-4fc103fef8db)

Loading it in QGIs shows large chunks of rivers missing

![image](https://github.com/osm2pgsql-dev/osm2pgsql/assets/1190866/1875ddeb-ba08-4d0b-90d5-ce57f975b57e)

I found a smaller river and looked at at z12, and similar problems are observed but they're not as severe

![image](https://github.com/osm2pgsql-dev/osm2pgsql/assets/1190866/08587480-74c3-4f0c-9dd6-9f6c259ba620)


## What did you do to try analyzing the problem?

I could see needing to adjust the zoom levels where the generalized tables start to be used by one, because the defaults could have been set for 256px tiles. But I tried that by looking at z7, and it was still a problem.

I tried a 25% buffer_size, and a 4096px image_extent. The latter helped slightly, but it was still a problem.


-- 
Reply to this email directly or view it on GitHub:
https://github.com/osm2pgsql-dev/osm2pgsql/issues/2087
You are receiving this because you are subscribed to this thread.

Message ID: <osm2pgsql-dev/osm2pgsql/issues/2087 at github.com>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/tile-serving/attachments/20230930/33d488e8/attachment-0001.htm>