Re: CADRG Drawing Decisions...

Hi Keith,

The CADRG projection is broken up into zones, 9 above the equator, and
9 below. The CADRG projection knows when it is in a particular zone,
and the RPFLayer will only display data for that zone. Each zone has a
pre-defined set of images, which may or may not exist, but each set
includes overlap images at the zone boundary. The overlap is generally
big enough to cover switching from one zone to another as you pan N-S,
at the base scale of the chart you are looking at - GNC = 1:5,000,000,
JNC = 1:2,000,000, etc. If you zoom out from that base scale and are
dancing around the zone boundary, you can get into a situation where
you are looking at the data bordering the overlap, and then the
projection switches zones, and you see the data from the other zone.

It would be nice if the layer scaled images from different zones to
fill in empty spaces. I'm not sure how much effort that would be to do.

  Hope this helps,

Don

On Tuesday, October 8, 2002, at 05:25 PM, Keith Baker wrote:

> How does the RPF layer decide which image to use. I have some
> wierdness
> were I see coverage for part of a map and not another... then I pan a
> little and can't see the section which had coverage. I suddenly have
> coverage where I didn't before... hurumpf...
> Keith
>
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Don Dietrick, BBN Technologies, dietrick@bbn.com
10 Moulton Street, Cambridge, MA 02138
617-873-3031 [fax]-2794
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