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Hi Chris and Andy,

Thank you for your suggestions. I was given just Lat/Long of ship's starting port and destination port in .CSV. Beside these I don't I have any additional information. Yes, prevailing winds and ocean currents will play a role in ships actual path but I think my collaborator is looking for the shortest distance just over water regardless of any other assumption that might affect on actual route. I haven't research at published route documents but this is worth trying. Projection is another issue since dataset has thousands of ports around the globe. I am thinking of  the "Merrcator Projection ?". I did a quick cost-path analysis for one of the ports pair. Due to lack of information to make a cost-raster ( I used just land and water mask as a cost raster) path tends to grip through land as below;


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Here voyages tends to pass very closely to land (mostly touches land mask). I am thinking to buffer land mask outward with X miles so that ships path will be X miles way from land. Also I am considering to bring ocean depth as another cost-raster if data is publicly available. Eventually, I am write a python script or run model builder once I figure out better way.  

I would like to hear more if anyone has any thoughts ! 

Thank you ! 
 

 

On Mon, Nov 10, 2014 at 11:38 AM, Andy Anderson <[log in to unmask]> wrote:
To remove the tedium, write a Python script.

Remember, though, that distance calculations depend on the projection you use. If you want the cost-path from, say, New York to Sydney, there is no single projection that will give you an accurate measure.

A better approach might be to determine the standard shipping lanes, calculate the distances (if you can’t find them in a table), and piece together routes.

More generally, you could set up an iterative algorithm to calculate distances using spheroid-based angular calculations with restrictions based on open water (e.g. at 40° north latitude, longitude will be restricted to roughly –74° to –9° and 128° to 140° and 142° to -124°).

— Andy

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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