[Mapit] Re: Map It

[Bernhard Reiter]

Hi James,

thanks for your interest in MapIt!.
I will also forward your question and my answer to the mapit
mailinglist.  http://intevation.de/mailman/listinfo/mapit
In general questions are answered faster on the mailinglist.



On Tue, Mar 13, 2001 at 01:09:28PM -0600, James Mullen wrote:
> I followed up on your advice and, I've looked at Map It.  I'm interested as
> to how I could use lat/lon for the coordinates instead of world coordinates.
> Or is it possible to convert lat/lon to world coordinates?  I have exactly
> no experience with GIS, the various data formats, and how to convert between
> them.

You have to decide for one flat (x,y) coordinate system.
In the configuration file (info) for the tiles you have to give
to specify the corners of each tile in this coordinate system.

For maps covering small areas you can use a lat long values in
decimal format as flat coordinate system.

> For my uses, I would like to use a database to serve the coordinate data to
> the map it application.  I could do this by creating a utility to create the
> data files with the appropriate values

You want to create the "markerdefs" file?
This is of course possible.

> Line 1 & 2 width and height of the individual tiles in pixels.
> Line 3  Block starts with a hash (#) character and two numbers that are the
> indices of the tile.
> Line 4, 5, 6, & 7 coordinates of the lower left and upper right corners of
> the tile.
> 
> Then repeat lines 3 thru 7 for each tile located in the directory.
> 
> Wouldn't this allow me to use Map It with my data without trying to modify
> the python code?

Yes, if you gave the right coordinates in the "info" files your
corresponding "markerdefs" files will work without projecting the
coordinates.

On the technical side note
that with FastCGI Installations, one MapIt! process only reads
the marker file once. You can use cgi with the current version,
but it will be slower of course.
If you modify the python code to directly query the marker database for
each request you can be faster.

Hope this answers your question,
	Bernhard

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