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Add function to calculate accessibility #169
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Although accessibility can be calculated from the travel time matrices produced by r5r, a dedicated accessibility function has many advantages:
Additionally, the new
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Conveyal documentation on decay functions is here. Those functions, beyond the step / cumulative opportunities function, are:
I think we have two options:
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I prefer exposing all decay functions and documenting what the parameter means in each case. Regarding the figure you posted above, are all of these "no accessibility islands" snap-related? The image seems a bit weird to me. Had we calculated the travel time matrices manually and calculated accessibility within R, the resulting plot would be similar? |
I would also prefer we expose all decay functions and create and I agree the maps has quite a few unexpected blind spots. Perhaps we should calculate accessibility step-by-step in R and compare agains the R5 estimates. |
Good points! The "inaccessible islands" of the previous maps happened because The resulting maps look the same. I've also compared both data.frames, and the accessibility values are exactly the same as well. I believe that using a frequency-based GTFS and larger number of Monte Carlo draws, there will be some variation in travel times and accessibility values, but in this simple tests all values are equal. |
Perfect. Thanks for looking into this, Marcus!Rafael H M Pereira
-------- Original message --------From: Marcus Saraiva ***@***.***> Date: 5/14/21 14:42 (GMT-03:00) To: ipeaGIT/r5r ***@***.***> Cc: Rafael H M Pereira ***@***.***>, Author ***@***.***> Subject: Re: [ipeaGIT/r5r] Add function to calculate accessibility (#169)
Good points! The "inaccessible islands" of the previous maps happened because max_walk_dist was set to just 300m. I've increased it to 1km and calculated accessibility again, using the two methods. Now the areas with "no accessibility" (dark grey on the maps below) are concentrated towards the southern edge of the city, which makes more sense.
The resulting maps look the same. I've also compared both data.frames, and the accessibility values are exactly the same as well. I believe that using a frequency-based GTFS and larger number of Monte Carlo draws, there will be some variation in travel times and accessibility values, but in this simple tests all values are equal.
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Simple demonstration of the effects of all decay functions on accessibility. |
To-do:
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I've added some more documentation to the function but I think we still have to provide (1) intuitive explanations to the behavior of each decay function, (2) the equations of each decay function |
@mvpsaraiva , I get the following error when I try to reproduce the example in the function:
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The issue seems to be in this line. I've removed the |
Thanks! I've just added a test script for the |
Setting this issue as priority, to be incorporated in the next package release. |
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