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map projection / poly fill bug [message #4021]

Wed, 19 April 1995 00:00

Ian E. Sprod
Messages: 12
Registered: February 1995

Junior Member

I have found a bug in IDL when plotting polygons onto
a map projection. If the polygon is on the edge of the
map then streaks of color are drawn from the edge of
the map to the edge of the screen Clearly the coordinate
mapping has gone awry in this case.

the following code demonstrates the problem :

-------------------------------------
pro poly_plot

; set co-ords for polygon in degrees

lat = [0,10,0,-10,0]
lon = [-10,0,10,0,-10]

map_set,10,0,/ortho,/cont,/noborder
loadct,5

; plot polygon
polyfill,lon,lat,color=50

; now put polygon at edge of plot

lon = lon + 85.0

polyfill,lon,lat,color=100

stop

end

---------------------------------------

Note I posted this one about 18 months ago and got a few replies
with ideas to filter out the "edge" polygons and not plot them.
This is not really a fix as the edge of the Earth on some
tilted Orthographic plots is not a simple meridian but some
ill-defined line I would rather not have to calculate.

Anyone else hit this problem?

Any answers? RSI?

Thanks,

Ian Sprod

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[Message index]

		map projection / poly fill bug By: Ian E. Sprod on Wed, 19 April 1995 00:00
		Re: map projection / poly fill bug By: Ian E. Sprod on Tue, 02 May 1995 00:00

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