Streetnames openstreetmaps more readable on Android

问题

I've build an Android APP with offline map data using Openstreetmaps and OsmDroid. On a device with MDPI 320x480 pixels the map looks OK, but on a device with a HDPI screen with 480x800 pixels the street names are small and a little bit harder to read them. My map data till zoom level 18, the maximum I could download and use with Mapnik tile source, is loaded as a zip-file from the SD-Card. My local maps are from a defined region of Brussels (Belgium).

A screenshot of an MDPI device with 320x480 pixels:

A screenshot of an HDPI device with 480x800 pixels:

If you see these views in the app on the device the MDPI map is good readable, in the HDPI map the street names are smaller.

Is there a way to make the street names also more readable on the HDPI device, so the user haves the idea that he zooms one step further on the map? Because it's not possible to go to zoom-level 19, because there is no openstreetmaps data for it. So a little workaround solution with easy and small implementation time/work my be OK for me. Zooming is now done by swiping on the map. If you also need the code, let me know and I'll post it.

Thanks in advance.

Kr

回答1:

Osmdroid works with tiles that are static PNG images. You can not change the tile images. If you want to have a better mapping solution try MapsForge. This app/library works with maps data and renders them dynamically. This way you have more control on rendering maps and you can customize its texts and fonts and colors.

回答2:

In this answer I will explain a little bit how I changed the size of the street names.

In the jar file of MapsForge there is a xml-file included that will standard be used for rendering the map data. You can download this file also by checking out the source code from the server: http://mapsforge.googlecode.com or download the xml-file itself from here: http://mapsforge.googlecode.com/svn/trunk/mapsforge-render-theme/src/main/resources/osmarender/osmarender.xml. So, you have a basic to tweak your own render file. I tweeked it a little bit like this:

(snippet of the xml-file):

On the Wiki-page of the MapsForgeRenderThemeAPI page (on the site above) you can find how to tweak your own render file and what e, k, v attributes in the rule element means. As you can see there is a rule element with e="way", k="area", v="~|no|false" inside the no-tunnel way rule-element somewhere under the way rule-element. Every rule-element under this element haves an e="way", k="highway" and v value equal to the openstreetmap parameters. As you login to the edit page on openstreetmap.org you can find out the kind of streets you want to tweak the names for.

Now I gonna tell how you can exactle the font-size you want for a specified type of street. As an example I will take the tertiary road element. Each kind of way rule-element contains some code like this:

<rule e="way" k="highway" v="tertiary">
    <line stroke="#ffff90" stroke-width="1.5" />
    <rule e="way" k="*" v="*" zoom-min="14">
        <pathText k="name" font-style="bold" font-size="32" stroke="#ffff90" stroke-width="2.0" />
    </rule>
</rule>

The line element specifies how the street will be displayed (color, width, black border, ...). There is again a rule-element inside here containing a pathText element. This element specifies how the text will be displayed inside the stroke(color, width, font-size, ...). So, this is the element we need! In my example, as you can see, the font-size for the street names for a tertiary road will be displayed with a size of 32 pixels for a zoom-in-level of 14 or higher.

Now we want to use our own render theme xml file:

I've added my own render-xml file in the assets folder of my project. Than a t launch time, I copy the file to a location from where I can read it out when it is needed. In the activity where you handle your mapsforge map you only have to link to this file by implementing code like this (example):

File f = new File(Environment.getExternalStorageDirectory(), myRenderTheme.xml);
mapView.setRenderTheme(f);

Note that setRenderTheme(File) will throw a FileNotFoundException.

So, this is all for changing the street names with mapsforge. You can render you're whole map as you want!

Thanks to the MapsForge development community.

Have fun!

Kr

来源：https://stackoverflow.com/questions/10883653/streetnames-openstreetmaps-more-readable-on-android