Determine the route a ship should take accounting for the ocean currents and the wind?

[wesape]

Hi! How the path distance tools work page (https://pro.arcgis.com/en/pro-app/tool-reference/spatial-analyst/how-the-path-distance-tools-work.ht...) gives out a few examples on how the path distance analysis could be used. One of them is determining the route a ship should take accounting for the ocean currents and the wind.

I think I understand the wind bit (calculate time to cross pixel from wind/ship speed and then use horizontal factor to take the directionality into account), but how exactly can the currents be added to the path distance tool? All help will be greatly appreciated!

[DanPatterson]

Most likely through the horizontal and vertical cost factors

How the horizontal and vertical factors affect path distance—ArcGIS Pro | Documentation

beyond distance between the cells, you would have to consider whether you were travelling with the current (lower cost) but had a wind in your face (higher cost).  These costs you would have to establish and associate with the directional component.  

This is where "human-ware" would have to intervene, unless you had a relationship between direction and the "cost" when the phenomenon was absent

[LizGraham]

Hi,

Hopefully you will find this information helpful as you perform your analysis:

• You will need to assume that the force of the wind and force of the current are constant throughout your study area.  Please refer to this blog: Creating accumulative cost surfaces using directional data 
• In order to take into consideration the direction of both the wind and the current you need to combine them before running the Path Distance tool, or the new Distance Accumulation tool.
• When you combine wind and current direction the resulting horizontal factor raster will need to show the direction of least cost travel considering both wind and current.
• Please note that negative value assigned to a horizontal factor cell ‘turns off’ horizontal factor function evaluation for that cell. (A negative value could represent that wind and current forces are equal but opposite at that cell and therefore horizontal factor force is not needed to be evaluated at that location). https://pro.arcgis.com/en/pro-app/arcpy/spatial-analyst/an-overview-of-horizontal-factor-classes.htm

I hope you find this information is helpful,

Liz Graham

[wesape]

Good morning!

Thank you both for your replies. Here are some additional thoughts:

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• You will need to assume that the force of the wind and force of the current are constant throughout your study area.  Please refer to this blog: Determine the route a ship should take accounting for the ocean  

My study area is large (India to China) so I would need both winds and currents to be variable. The blog link you provided links back to this discussion, could you repost it please?

• In order to take into consideration the direction of both the wind and the current you need to combine them before running the Path Distance tool, or the new Distance Accumulation tool.
• When you combine wind and current direction the resulting horizontal factor raster will need to show the direction of least cost travel considering both wind and current.

This is the bit I am having the most problems in. As far as I understand, the horizontal factor would be used to take into account the effects of wind directionality while sailing: for example it is easier to sail when you are in broad reach and harder when close-hauled (see Alberti 2018, TRANSIT: a GIS toolbox for estimating the duration of ancient sail-powered navigation, https://www.tandfonline.com/doi/full/10.1080/15230406.2017.1403376, p. 515-517/p. 6-8 in PDF/chapter 3 on the HTML version). The currents instead would push you in the same way regardless of the direction. If I were to sum winds and currents together, then the currents would also be affected by the horizontal factor? Could also very well be that my thinking is way off and I am missing something...

Looking forward to more comments!

Wesa 🙂

[LizGraham]

Hi Wesa, I have updated the blog link in my comment above. Thanks, Liz

[wesape]

Thank you! I started wondering if it would be possible to somehow turn the current speed & direction into a DEM/slope and use that in path distance? Perhaps that way it would be independent of the wind related calculations?