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Posted by Captain Paralytic on 07/12/07 11:56
On 12 Jul, 12:50, busnet <goo...@00l.de> wrote:
> Hi.
> I've got the following problem: I have a huge xml-file that represents
> a street map of a city. Each street is stored as a couple of
> coordinates (start, end and all the turns).
> When I set a marker in a google map, I want to find all streets that
> are near this marker position.
> I now parse the whole file as a simpleXML object, and calculate the
> distances to each street segment (using linear algebra algorithms,
> that is, constructing the vector from two points and computing the
> distance from the given point to this vector).
> Up to now it works like this: I set a marker and the gmaps method
> "gdownload()" calls a server side php script, which
> 1. reads the xml file into an simplexml object
> 2. for every two coordinates that belong to the same street, it
> calculates the vector and computes its distance to the point
> 3. returns the nearest x streets (as polylines) back to the client
>
> It repeats this, when I set the next marker.
>
> Problems/need for ideas:
> 1) It always reads the XML file anew, when I set another marker. Is
> there some way to cache this or a more intelligent approach? I tried
> saving the whole Simplexml-object in a session variable, but it was
> too huge. I guess I could create some tables in mysql, but I'm not
> sure thats the best solution yet.
> 2) Not php-specific: Do you have any ideas how to speed up the process
> of finding the nearest lane(s)? I tried to consider only those streets
> whose endpoints are within a certain range from the given marker-
> point, but it was not considerably faster and if there was a street
> thats very long and straight the endpoints may be far away, but the
> street itself is quite near.
ISTR this haveing been discussed in comp.databases.mysql recently. Do
a google search over there.
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