least cost path restricting travel direction

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04-03-2018 08:45 AM
New Contributor II

I've successfully calculated anisotropic least cost paths using vertical factor tables (Tobler's Hiking Function Towards and Away created by Nicholas Tripcevich, Ph.D., University of California, Berkeley (2009), developed from Tobler. Original Webpage: <http://mapaspects.org/node/3744>) - the fastest routes.

And, for comparison, I've calculated isotropic least cost paths using slope only (least slope) - the easiest routes.

I'd now like to calculate several least cost paths within a group of 11 points (sites) that restrict travel direction - no travel to the east -  and use least slope. Travel would be from one point - the easternmost in the group - to all the others which lie west. Presumably I would need to use the horizontal factor parameters, but not exactly sure how to begin - also wondering if simply restricting the processing extent in environments would provide the same or similar results.

Thank you,

Susan

PS-Using least slope only as the only factor with these particular points and geographic region (with river and lake valleys and mountains)  produces LCPs that are nonsensical - traveling eastward and northward following the lowest-lying river valleys hundreds of miles out of the way; thus the rationale for restricting travel east.

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MVP Esteemed Contributor

Path Distance... a related tfunction will allow you to accommodate slope and directionality in a cost analysis

New Contributor II

Dear Dan,

Thank you very much for your reply.

I should have been more explicit: I use the Path Distance tool first to create distance rasters and backlink rasters before using the Cost Path tool. I only have experience, however, using the vertical factor parameters (and then, only with the table, using Tobler’s Hiking Function). I do not have any experience with setting the horizontal factor parameters (which I believe I would need to constrain travel direction to everywhere but the east) – and I am having difficulty interpreting the help – this is what I am asking for advice.

Thank you,

Susan

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MVP Esteemed Contributor
New Contributor II

Yes, that’s the “help” I am struggling with – thank you.

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MVP Esteemed Contributor

The easiest way is to go with the pictures of the car then switch over to the bobcat explanations here

http://pro.arcgis.com/en/pro-app/tool-reference/spatial-analyst/how-the-source-characteristics-affec...

If you are working with an origin cell, then that makes things easier to understand.  So if you just can't move in a particular direction the 'graph examples' will basically should you that aspect.  The 'cost of moving in a particular direction relative to it can be derived and your 'field of view' (ie preferred direction) will be considered.  So if you can only move East-ish from an origin, then it should be apparent that moving due East will have the least cost with respect to direction.  A horizontal angle (field of view) will have different 'costs' since they are at different angles relative to the source cell and relative to the field of view.  Sooo. Start at a point, look at the equations and the figures since it is a 2 step process

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