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11Bravo · 05-05-12, 10:35 AM

The U-13 is on its 3rd pre-war voyage to develop navigation tools for the war. This mission is to better understand the Nautical Chart, especially the map projection and how how it relates to Celestial Navigation.

The demonstration of the 3-star shoot at the end of the last voyage revealed that a correction factor to longitude was necessary. This mission tests that concept by conducting several 3-star shoots at varying latitudes.

I will choose assumed positions on either side of the observing position. One assumed position will be 1° West and North of the observing position, while the other will be 1° East and South of the observing position. We will plot the error triangles for both assumed positions. We will also correct the longitude of the error triangles using the 1/cos or sec of the assumed latitude.

If the assumed map transformation is correct, we should see the error triangles diverge from the observing position as we increase latitude. If the correction factor is correct, we should see the corrected positions move back to where we know they should be.

I think the map transformation is this cylindrical equidistant projection. The equations are shown on the figure.

You can read more about it at the following links

http://mathworld.wolfram.com/Cylindr...rojection.html
http://mathworld.wolfram.com/Equirec...rojection.html
http://en.wikipedia.org/wiki/Equirectangular_projection

05-05-12, 10:35 AM	#96
11Bravo Medic Join Date: Dec 2006 Location: Error Triangle Posts: 168 Downloads: 157 Uploads: 0	The U-13 is on its 3rd pre-war voyage to develop navigation tools for the war. This mission is to better understand the Nautical Chart, especially the map projection and how how it relates to Celestial Navigation. The demonstration of the 3-star shoot at the end of the last voyage revealed that a correction factor to longitude was necessary. This mission tests that concept by conducting several 3-star shoots at varying latitudes. I will choose assumed positions on either side of the observing position. One assumed position will be 1° West and North of the observing position, while the other will be 1° East and South of the observing position. We will plot the error triangles for both assumed positions. We will also correct the longitude of the error triangles using the 1/cos or sec of the assumed latitude. If the assumed map transformation is correct, we should see the error triangles diverge from the observing position as we increase latitude. If the correction factor is correct, we should see the corrected positions move back to where we know they should be. I think the map transformation is this cylindrical equidistant projection. The equations are shown on the figure. You can read more about it at the following links http://mathworld.wolfram.com/Cylindr...rojection.html http://mathworld.wolfram.com/Equirec...rojection.html http://en.wikipedia.org/wiki/Equirectangular_projection __________________ "Sounds of terror are in his ears; While at peace the destroyer comes upon him." -- Job 15:21 Last edited by 11Bravo; 05-05-12 at 10:45 AM.