http://techbase.kde.org/index.php?title=Projects/Marble/GeoPainter&feed=atom&action=history 2013-05-20T02:08:47Z Revision history for this page on the wiki MediaWiki 1.20.2 http://techbase.kde.org/index.php?title=Projects/Marble/GeoPainter&diff=69144&oldid=prev 2012-03-01T21:56:09Z

<p>Created page with &quot;= Notes about GeoPainter = == Concepts == Horizon is a spherical projection concept to decide if a point is on the viewer&#039;s side or the other. It is NOT dependent on viewpor...&quot;</p> <p><b>New page</b></p><div>= Notes about GeoPainter =<br /> <br /> == Concepts ==<br /> Horizon is a spherical projection concept to decide if a point is on the viewer's side or the other.<br /> It is NOT dependent on viewport visibility<br /> <br /> Dateline is a repeatX issue, so that a line crossing the dateline does not lead to a tear the whole map wide<br /> <br /> Pole is an issue for projections which cannot draw it as a point (or even not at all)<br /> <br /> Projection Drawing depends on tessellation<br /> Tessellation is a geodetic issue, determining how to connect points. Options:<br /> NoTessellation: straight screen coordinates lines between projected points<br /> Tessellate: great circle line between projected points<br /> needs horizon and dateline check<br /> FollowLatitude: special case when latitude is same, walk on the latitude circle<br /> <br /> do we need rhumb line (line of constant compass course)??<br /> <br /> Need to keep in mind that tessellating must keep polygons that still allow fill.<br /> <br /> == Current code ==<br /> - systematically looks for poles and datelines, splitting the polyline into ones which don't cross idl or pole<br /> <br /> - looking for datelines is a recursive calculus to identify latitude at which the idl is crossed<br /> <br /> - iterates all points, determines<br /> - if horizon is crossed<br /> - if and which tessellation is needed<br /> - adds points to one QVector&lt;QPointF&gt;<br /> <br /> == Complications ==<br /> - looking for dateline is not necessary for Spherical, very hard for NoTessellation (screen vs Geo space)<br /> <br /> - because of repeatX we calculate all possible points depending on viewport radius, then let painter frame down to visible viewport</div>

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