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I using microsoft visual 2010 with dynamic data display dll I need to do an circle around a point by angle and radius. I have been successful but it's wrong, I think so. First of all, my source code:

I got the prePs from the mouseClick (it's not problem the point is perfect working you can see next in the picture)

 // Get the X position of the pointClicked
                    cx = (double)prePs.X;
                    // Get the Y position of the pointClicked
                    cy = double.Parse(this.plotter.Viewport.Transform.DataTransform.ViewportToData(prePs).Y.ToString());

                    // Get the new X position of the pointClicked by the angel with math calculation
                    xEndP = (float)(double.Parse(txt_enterRadius.Text.ToString()) * Math.Cos(a * Math.PI / 180F)) + cx;
                    // Get the new Y position of the pointClicked by the angel with math calculation
                    yEndP = (float)(double.Parse(txt_enterRadius.Text.ToString()) * Math.Sin(a * Math.PI / 180F)) + cy;

Secondly what I actualy got : At the middle I got exactly perfect circle, but in the north and south the circle is type of ellipse. picture:

http://sizmedia.com/my.php?i=hm2zuv5yyenj.png

I would happy to understand : Why? Is it good? Or I need to change something? Becuase i thought about it and the Earth is circle and its type of reasonable.

SurvivalMachine
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Ben Tubul
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  • The map projection is likely the Mercator projection and so what you are seeing is the correct representation of a circle on a distorted representation of the surface of the Earth. The Mercator projection "unwraps" the planet in a cylinder fashion therefore as you move further from the equator towards the poles, the land mass is distorted. You can see by the markers at the left of the map, the distance between 0 and 30 degrees is much less than the distance between 30 and 60 degrees. – Charleh Sep 21 '14 at 18:15
  • See here: http://en.wikipedia.org/wiki/Mercator_projection – Charleh Sep 21 '14 at 18:16
  • This is a more accurate representation of the actual land mass area of the earth - as you can see, towards the poles, land is a lot smaller than on the Mercator projection: http://www.viewsoftheworld.net/wp-content/uploads/2010/08/worldmapper_basepeters.jpg – Charleh Sep 21 '14 at 18:19
  • And finally this is one of my favourite projections: http://www.viewsoftheworld.net/wp-content/uploads/2010/08/worldmapper_basefuller.jpg - gives you a really good idea of the relative land-masses – Charleh Sep 21 '14 at 18:22
  • So if i understand good its right and nothing to change ? : ) – Ben Tubul Sep 21 '14 at 22:21
  • Thanks again, may you know how to get distance between 2 points *on map* then its no the regular calculate distance 2 point ....... – Ben Tubul Sep 21 '14 at 22:36

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