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mesh domain spanning hemispheres at 180E


Mark Prater
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I am trying to develop a mesh that spans the eastern and western hemispheres at 180E, and I am (or SMS is) having some difficulty with the input coordinates. I've played with several test domains to understand my problem, and have found out that

( test 1) I can easily create a mesh when the domain is entirely in the western hemisphere, and my *.cst and *.pts file longitudes are specified in negative degrees east (that is, Seattle, USA is -122.33E).

(test 2) I can easily create a mesh when the domain is entirely in the eastern hemisphere, and my *.cst and *.pts file longitudes are specified in positive degrees east (that is, Tokyo, Japan is 139.69E).

(test 3) I have not been able to create a mesh when the domain is entirely in the western hemisphere, and my *.cst and *.pts file longitudes are specified in positive degrees east (that is, Seattle, WA is 237.67E). I can load my *.cst file without problem, but when I "Select Feature Arc" and click on my domain boundary I get an error message that states "Encountered an improper argument." Any attempt to re-project the data to a UTM zone produces the same error message, and the data is not re-projected

(test 4) When I attempt a cross-hemisphere domain with my *.cst and *.pts file longitudes specified in positive degrees east, I get the same failures as in test (3).

(test 5) When I attempt a cross-hemisphere domain with my *.cst and *.pts file longitudes specified in negative degrees east, I get the same failures as in test (3).

So, my specific questions are

(1) Can I use Geographic coordinates in my *.cst and *.pts files for a domain that spans hemispheres at 180E? If yes, how? If not, what coordinate system do you suggest?

(2) What re-projection Cartesian coordinate system do you recommend for smoothing data sets and for the actual mesh generation (Map -> 2-D Mesh)?

Thanks!

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One additional note: I thought I would be clever, so I shifted all the longitudes in my *.cst and .pts files to be centered around the zero meridian rather than around 180E. That seemed to solve my initial problems, and I was able to generate a mesh. However, I got the same "Encountered an improper argument" when attempting to re-project from the UTM zone back to geographic coordinates. Also, I played with the USGS version of Global Mapper to see how it deals with crossing hemispheres at 180E. If I load my *cst file with all positive longitudes, I see a "Coordinate out of range" message for points greater than 180,. Likewise, if I load my *cst file with all negative coordinates, I see a "Coordinate out of range" message for points less than -180. So, the Global Mapper utility is also bothered by crossing the 180 meridian.

Cheers,

-- Mark

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I can now generate a hemisphere-spanning mesh by performing the coordinate projections and re-projections external to SMS, and use SMS only for the mesh generation. Within SMS I set my projection to "Local projection" with the units set to "Meters".

I'm still curious if there are better ways to do this entirely within SMS.

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