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Radial Madness


Change in Latitude, Change in Attitude
As I am prone to jabber on about from time to time, one of the characteristics of the resurgent Mercator map projection is the relative difference in size that it represents equally-sized things, depending on latitude.  Quick lowdown: stuff at the equator appears the smallest, while the farther you go north or south from the equator the same-sized stuff appears bigger.  This has led to some questions in our training sessions around a new feature in VFX 4

The Radius Query
One of the tools available in VFX 4 is a generic drawing tool that can be used to feed a radial spatial query.  You swipe out a distance and VFX throws over the wall a set of geographic coordinates for you to query against for whatever reason (with the provision that it be used for good instead of evil).  You can drag the query rings around, too, to reposition them to somewhere else on the map -good for what about here, what about here, what about here scenarios.  So if you swipe out a query area with a 500 mile radius and then drag it all over the map, we maintain the 500 miles, even though the circle grows and shrinks as you move it about.  It looks kind of funny, but it is a good thing.

Heads Up!

Here, I drew two queries -both of them have a 500 mile radius.  The nature of the Mercator projection makes the radius up near Greenland massive relative to the one near Africa.  C’est la vie.

John Nelson / IDV Solutions / john.nelson@idvsolutions.com


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