I am trying to customize an Albers and a Hotine Oblique Mercator (HOM) projection to minimuze distortion in the region I am analyzing. The region extends from about 51 to 62 degrees latitude, covering an area about the size of the Ukraine. The region is oriented NW - SE.
I want to make sure I am using correct methods for determining the two projection parameters: lat/long of the projection center, and centerline azimuth. I am using ArcMap v10. Here's the procedure I've followed so far:
I am hoping there are some projection experts out there that can tell me if the above procedure, especially Steps 3 and 4, is a correct way to determine the needed projection parameters. Am I on the right track? Is it correct to be determining the center on the spheroid and the angle of the geodesic from the center point (instead of a "2d" geometric center and azimuth)?
I hope the problem description was clear. I'm eagerly looking forward to any answers, tips, discussion, etc.!
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I want to make sure I am using correct methods for determining the two projection parameters: lat/long of the projection center, and centerline azimuth. I am using ArcMap v10. Here's the procedure I've followed so far:
- Created a single polygon that defines the analysis region (by, generally,creating a convex hull around the extent of the watersheds coveringthe region). This polygon is the area I am customizing theprojection for.
- Projected the polygon to Geographic/NAD 83.
- Used Jeff Jenness' Tools for Graphics and Shapes
(http://www.jennessent.com/arcgis/shapes_graphics.htm) to determinethe polygon's center of mass on the GRS80 spheroid. The resultingcoordinates are what I used for the "projection center" parameter. - To determine the centerline azimuth, I first projected the polygonto an azimuthal equidistant projection, specifying the projectioncenter at the coordinates determined in Step 3.
- Then I drew a polyline (in the azimuthal equidistant projection),snapped to the projection center point, representing the directionaltrend of the region polygon. To get the azimuth at the projection'scenter, I used Jeff Jenness' Tools for Graphics and Shapes todetermine the beginning azimuth of the geodesic curve at the centralpoint.
- For the Albers projection I am using the longitude for theprojection center, as determined in step 3. Am also using the awesome spreadsheetcreated by Bill Huber (http://forums.esri.com/Attachments/34278.xls)to determine where to place the standard parallels to minimize thescale distortion within the polygon region.
I am hoping there are some projection experts out there that can tell me if the above procedure, especially Steps 3 and 4, is a correct way to determine the needed projection parameters. Am I on the right track? Is it correct to be determining the center on the spheroid and the angle of the geodesic from the center point (instead of a "2d" geometric center and azimuth)?
I hope the problem description was clear. I'm eagerly looking forward to any answers, tips, discussion, etc.!
أكثر...