FAQ index
1. Into which directory should the Fetch_map ZIP package be extracted?
Fetch_map is not dependent on the directory path you extract the package
to. Extract the package to any location in your directory structure.
Only requirement is that you know where your Python installation is when
starting the Fetch_map application.
Below are listed the requires steps to use the application (prerequisites are
to have the Python interpreter correctly installed on your machine and
the Python Imaging Library installed to your machine)
- Extract the Fetch_map ZIP package to your disk where ever you like
- Enter the
fetch_map directory created with the package
- Start the application using your Python interpreter. Have the Python
set up in you PATH environment variable or give the location explicitely
on the command line as in the example below.
Example:
C:\> cd work\maps\mobile
C:\work\maps\mobile> unzip c:\temp\fetch_map.zip
C:\work\maps\mobile> cd fetch_map
C:\work\maps\mobile\fetch_map> C:\Python24\python fetch_map.py -s rka Pirkkala 6815986 2480962 6.0 5.0 1:50000
2. Why is the delay between fetched map tiles only few
seconds using the retkikartta.fi and a lot longer with the
Karttapaikka? Is this a bug?
This is not a bug. The delay was introduced initially because
some people were mass downloading unnecessarily large maps from the
Kansalaisen Karttapaikka. The Karttapaikka suffered load problems
due to fetch_map usage and therefore I altered fetch_map to
include a random 30 to 60 second delay between fetched map tiles.
The Karttapaikka map tile is 600x600 pixels of size. The Retkikartta.fi
map tile is 256x256 pixels, which is only about 18.2% of the area
the Karttapaikka map tile covers. In addition to this, in my
reverse engineering experience, the Retkikartta.fi map tiles are static
so the remote map service does very little or no computing to serve
one map tile to fetch_map. On the other hand the Karttapaikka tiles are not
static and involve at least some processing in the remote end. Therefore
I estimated that the load with the Retkikartta.fi service is at most half
of the load in the Karttapaikka.
Half of the 18.2% "load" is 9.1% (about 10%). Thus I use 10% of the
delay with the Retkikartta.fi, ie. a random 3-6 second delay.
3. How do I configure http proxy settings for fetch_map?
If you want or need to use a proxy server to access map sites, you can set
the http proxy for fetch_map by declaring an environment variable
"http_proxy". This can be done from command line before launching fetch_map
or by configuring permanent user or system environment settings.
Example: (Windows command line)
C:\work\maps\mobile\fetch_map> set http_proxy=http://my.proxy.com:8080/
C:\work\maps\mobile\fetch_map> python fetch_map.py -s rka Pirkkala 6815986 2480962 6.0 5.0 1:50000
