[OT] Navigation systems

[Peter Haworth]

Thanks Alex, I'll check it all out.

Now I understand a bit more about this, I may have a use for it. A project
I'm working on requires figuring out how to navigate from one table to
another in an SQL database using defined foreign keys between intermediate
tables. Right now, I'm just trying all possible routes but maybe these
navigation techniques could help.

Pete
lcSQL Software
On Oct 17, 2013 8:32 PM, "Alex Tweedly" <alex at tweedly.net> wrote:

> On 17/10/2013 16:57, Peter Haworth wrote:
>
>> Thanks for the pointers eveyone.  I have some reading to do!
>>
>
> I'll suggest some more reading :-)
>
> I don't agree with some of the earlier posts. Navigation problems (i.e.
> 'best' route from A to B) is not equivalent to the Travelling Salesperson
> Problem - it's considerably easier than that. It's a graph searching
> problem, and so there are solutions which run in polynomial time (whereas
> NP-complete problems like TSP don't).  Best known approach would be
> Djikstra's algorithm ( as used in in network routing, like OSPF and IS-IS)
>
> You could start with http://en.wikipedia.org/wiki/**Dijkstra%27s_algorithm<http://en.wikipedia.org/wiki/Dijkstra%27s_algorithm>though it's a pretty hard slog.
>
> An easier intro is in http://en.wikipedia.org/wiki/**Link_state_routing<http://en.wikipedia.org/wiki/Link_state_routing>  and go down to the section on "Calculating the shortest paths" (and don't
> get distracted by all the rest of the stuff link-state routing has to deal
> with;  in map/directions you don't need to dynamically detect link failures
> and you don't need to spread info about them over the network you are
> trying to use :-)
>
> Or, jump to the answer  ...
> http://stackoverflow.com/**questions/430142/what-**
> algorithms-compute-directions-**from-point-a-to-point-b-on-a-**map<http://stackoverflow.com/questions/430142/what-algorithms-compute-directions-from-point-a-to-point-b-on-a-map>
>
> -- Alex.
>
>> Mike,  I never made the connection between aircraft boarding and
>> navigation
>> before but you opened my eyes!  Incidentally, Southwest now have a "clump"
>> system layered on top of their no seat allocation rule. There are three
>> boarding groups (A,B,C) and within those groups, numbers from 1-60 (or
>> more
>> for larger aircraft), with the group and number being assigned serially (I
>> think) in order of time checked in. The numbers aren't seat numbers, just
>> sequence numbers within the group. At boarding time, group A, numbers 1-30
>> go first, followed by group A numbers 31-60, and so on.
>>
>> This all came about really because I'm using my Nexus 7 for navigation and
>> it does not have the LTE option on it so I'm not on the internet when
>> driving.  I found a few apps that will provide navigation when not
>> connected to the internet, which they do by downloading maps from an open
>> source mapping project.  Obvioulsy you have to get the necessary maps
>> while
>> you have an internet connection but after that, the apps use the gps in
>> conjunction with the maps to figure out routes and navigate them.
>>
>> I guess Google maps allows you to save maps and work offline but I found
>> that it has size restrictions that won't save maps that cover a large
>> area.
>>
>> Pete
>> lcSQL Software <http://www.lcsql.com>
>>
>>
>> On Thu, Oct 17, 2013 at 7:57 AM, Richard Gaskin
>> <ambassador at fourthworld.com>**wrote:
>>
>>  A good overview:
>>> http://en.wikipedia.org/wiki/****Travelling_salesman_problem<http://en.wikipedia.org/wiki/**Travelling_salesman_problem>
>>> <h**ttp://en.wikipedia.org/wiki/**Travelling_salesman_problem<http://en.wikipedia.org/wiki/Travelling_salesman_problem>
>>> >
>>>
>>> --
>>>   Richard Gaskin
>>>   Fourth World
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