[Qgis-user] Distance matrix using shortest path (FH longest path and others)

[Nicolas Cadieux]

 Hi,

My answer pertain to vector based road or river networks.  Least cost and circuitscape are generally raster based analysis.  Maybe you should post on a new email so we don’t mix up both topics.
Cheers!

Nicolas

> Le 26 août 2019 à 14:28, Falk Huettmann <fhuettmann at alaska.edu> a écrit :
> 
> Dear all,
> thanks indeed,
> we want to optimize for the longest path, or the one with the most habitat/pixels underneath,
> or at least see all options.
> It's opposite from 'minimizing'.
> I am probably aware how it is computed, mathematically (=flip the optimization),
> but in case you already know or see a plug-in, or such tools and software available please kindly advise.
> 
> Very best and thanks
>       Falk
> 
> PS There is a lot of philosophy showing how utterly poor those optimization
> and mindless cost/benefit tools perform in real life (=Pareto optimum described as a 'brutal racist' tool etc
> See failures of Economy or when it gets applied to humans).
> It's also utterly harmful for wildlife corridors (as wildlife then is just EXCLUDED and MINIMIZED,
> instead of maximized. Just think of Movement Paths for Elephants and computed with 
> Least-Cost Paths, or Circuitscape. It's pathetic. That's why economic developers and NGOs like those tools so much. 
> So instead here we are looking for other options and readily-available tools, ideally. QGIS could be a good platform for that.
> Thanks.
> All of this has real-world implications (urban planning, road projections, logistics landscape design,
> national park design etc)
> 
> 
>> On Mon, Aug 26, 2019 at 10:14 AM Nicolas Cadieux <nicolas.cadieux at archeotec.ca> wrote:
>> Hi,
>> 
>> Shortest path analysis can be done by counting the number of nodes (connections or intersections) or by using a distance variable (traditionally length).  However, “length” can be anything.  It can be any combination of factors.  Therefore, if you can model the various factors in a single “length” variable, then you can find the best path for your model.  Some algorithm will give you all paths to one point, some only the shortest path, and some will permit you to use a maximum cut off (ie max radiation absorption dose if radiation is part of the model.)
>> 
>> Nicolas
>> 
>>> Le 26 août 2019 à 13:43, Falk Huettmann <fhuettmann at alaska.edu> a écrit :
>>> 
>>> Dear Kind Colleagues,
>>> 
>>> thanks, I have a similar question, but with an opposite aim:
>>> 
>>> We have two points, 
>>> and want to connect them,
>>> but then, NOT with the most direct and shortest path.
>>> Rather, with the most meaningful and considerate one.
>>> Like,
>>> length is not to be penalized but other factors, habitats available, amount of pixels
>>> underneath etc.
>>> Perhaps even showing different scenarios (aka, many paths lead to Rome...) ?
>>> The path can consist of more than a line, an area connection let's say.
>>> 
>>> So in other words: the optimization is NOT done by short distance.
>>> 
>>> Would you have any ideas and suggestions on that ?
>>> 
>>> Thanks so much for any input
>>>    Falk Huettmann 
>>> 
>>> 
>>> 
>>>  
>>> 
>>> 
>>>> On Mon, Aug 26, 2019 at 2:07 AM Chintan Advani <chintanadvani at gmail.com> wrote:
>>>> Hi guys,
>>>> 
>>>> I have a shape file with set of points on a road network. I am trying to find the shortest distance among these points using the shortest path tool. I have tried using the distance matrix tool in QGIS but it gives eucledian distance between these points whereas I am looking the path distance (based on road network). Can someone please suggest some tool or technique that can help me solve this problem?
>>>> 
>>>> Thanks and Regards,
>>>> __________________________________________
>>>> Advani Chintan Sanjeev
>>>>         Research Scholar,
>>>>         Civil Engineering and Build Environment,
>>>>         Queensland University of Technology, 
>>>>         Brisbane-4000, Australia.
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