Zoom level concept ?

[fzk]

Hi all,

I'm trying to unterstand the mapsforge concept for zoom levels.

I have found three places concerning zoom levels:

1. tag_mapping.xml (eg. osm-tag key="waterway" value="riverbank" zoom-appear="8")

2. configuration for mapfile-write (zoom-interval-conf, eg. 5,0,7,10,8,11,14,12,21)

3. theme.xml (eg. rule e="way" k="oneway" v="yes|true" zoom-min="16)

My interpretation:

1. Controls the objects to store in in the .map-file and sets a default zoom level.

2. Purpose unclear.

3. Controls the apperance for each object in each zoom level (starting at the default zoom level).

Questions:

- How to interprete the "zoom-interval-conf" for the mapfile-writer ?

- And how does the configuration affects the zoom control in "tag_mapping.xml" and "theme.xml" ?

- What else is important to know ?

Thanks for any explanation ...

Regards Klaus

[Thilo Mühlberg]

Hi Klaus,

please refer to
https://code.google.com/p/mapsforge/wiki/SpecificationBinaryMapFile for
description of the current map file format. The idea of zoom intervals
is described there.

The configuration of the map-writer is independent from the
render-theme. You can configure the map-writer to assign objects a
certain zoom level which controls how they are stored in the map file.

On the other side, the zoom level in the render theme controls if a map
feature will be rendered at a certain zoom level or not.

If the map-writer stores a POI for zoom level 16, then the map-reader
will only read it for queries on zoom level 16 or higher. The render
theme might have a rule which says that such POIs should already appear
on zoom level 15, but these rules are only applied on the POIs and ways
which the map reader returns.

Greetings,
Thilo

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