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Distance of ocean path problem

Question asked by geonetadmin on Dec 25, 2012
Latest reply on Feb 13, 2013 by jhp7e
Original User: asancheti

Hello Everyone,

I have a problem which I am having trouble figuring out a solution for. I think the point I'm stuck on is relatively simply compared to the problem itself.

Problem: I have a series of lat-long points which span the entire planet, these are about 200 points. I want to find the distance between every one of these points and every other point. So I have 208! permutations. The tricky part is that all of these points are in an ocean and the distance needs to be the distance of the shortest water only path between the two points.

I think I have this essentially figured out by adapting instructions from

http://www.biology.ualberta.ca/gis/uploads/instructions/AVMeasureNonLinearDistances.pdf

into the current ArcMap and automating using a python script (attached). As I understand it (my first GIS problem so be easy on me) you use an ocean raster to create a cost allocation raster and a backlink raster (whatever that is) on a particular source point. Then for each other point use costPath on the previously made raster layers, convert this costpath raster to a polyline and then calculate the length of it.

All this seems to be fine and indeed kind-of works except that the process does not take into account that the world is a sphere. In an extreme case two points that are really next to each other are calculated as the entire earth's circumference apart. Please see attached picture as a visual on what I mean, it is a screenshot of the output of the cost allocation raster process on the highlighted point you can see that the yellow circle indicating a small distance should extend east and wrap to the left side of the layer.

Does any one have any suggestions/help for me?

Thank you.

[ATTACH=CONFIG]20187[/ATTACH]

[ATTACH=CONFIG]20186[/ATTACH]

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