To slightly digress from the original topic, I think there’s a couple of geographic capacity questions that have to be asked in relation. I did a study on Port Efficiency and modeling way back in grad school – and it was much more pure geography than GIS. I apologize if this covers ground that is not elsewhere mentioned.

There’s the pure distance question: Using Arc of Circle type calculations is the distance, rather than straight line, as we’ve referenced here. I would generally argue Andy’s methodology is correct.

Secondly, there’s the capacity question: All ports have capacity ratings. For example, Shanghai, Hong Kong and LA will have larger capacities than perhaps a smaller like Port Angeles, WA or Ningdei, China. This is important to ask because it obviously changes routes.

Third, there is the trip purpose question: Is the goal to bring a Super-Panamax vessel to a large port where the shipments will be split into smaller, inner-ocean carriage vessels? If so, the trip becomes a question of which port is quickest to service that kind of division of cargo.

Finally, a major issue may be turnaround or efficiency time: A superior port with notable high speeds in turning around load exchanges may offer an incentive (time = money) that distance alone cannot model. I found this to be the case in Kelang, Malaysia.

I wish you the best of success, Milan, with your study.

Kind regards,

Rich

From: Northeast Arc Users Group [mailto:[log in to unmask]] On Behalf Of Shaun Walbridge
Sent: Tuesday, November 11, 2014 2:09 PM
To: [log in to unmask]
Subject: Re: Finding Distance between points over water

I’ve done some work on global modeling of ship movement, and can confirm this is a tricky problem. The ultimate solution that I ended up using was a weighted graph structure to connect adjacent ‘cells’ of the ocean. This has the advantage of not requiring arbitrary new calculations for any new pair of points, and can vary in resolution. The edges are then weighted by their geodesic distance, so that cost calculations are ‘true’ and not fixed to any single projection. Some details here.

cheers,

Shaun

-- 

Shaun Walbridge | GIS Engineer

On Nov 10, 2014, at 9:13 AM, Milan Budhathoki <[log in to unmask]> wrote:

Looks like email that I sent yesterday didn't go through. 

Here it is again: 

Hello Listserv,

I have point dataset of ship trips from one port to another. I want to calculate the shortest distance between each port pair  over water. There are thousands of voyages, and 5,000 unique ports from all over the world. One of the approach I can use in ArcGIS  is to run the Cost-Path tool having water/land as a cost raster to make a path only on water. But I assume that the Cost-Path approach would be little tedious for a large dataset. I wonder if anyone in this forum has a suggestion to calculate a shortest distance between two points having restricted path.

I will highly appreciate your feedback.

-- 

Milan Budhathoki

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--

Milan Budhathoki

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