RE: [OpenMap Users] What does the scale *really* represent?

Don,

I am curious about this as well. I need to provide a drag-zoom capability
to a server-side web-based OpenMap servlet I am working on, and I'm not sure
how to calculate scale based on minlat, minlon, maxlat, maxlon.

Can you elaborate specifically on how this can be calculated.

-----Original Message-----
From: Don Dietrick [mailto:dietrick@bbn.com]
Sent: Tuesday, February 11, 2003 10:46 AM
To: Matt McKeon
Cc: openmap-users
Subject: Re: [OpenMap Users] What does the scale *really* represent?

Hi Matt,

On Monday, February 10, 2003, at 12:08 PM, Matt McKeon wrote:

The scale is based on the
com.bbn.openmap.proj.Planet.defaultPixelsPerMeter (= 3272) setting.

Each OpenMap projection uses this constant as a basis of creating pixel
spacings relating to scale, usually in the computeParameters() method
of a Projection.

Hope this helps,

Don

>
> Hi folks. I have a question about the mathematical foundations
> of the scale value in the Projection interface.
>
> I'm trying to puzzle out how one would write an adapter from
> a reasonable subset of the OpenGIS coordinate transform API
> to OpenMap's projection API. I believe that scale in an OpenGIS
> ProjectedCoordinateSystem object is represented as
> meters / unit (aka pixel). The OpenMap API docs claim that
> the scale value of a Projection is represented as pixels/meter.
> However, in the list archives, Don says something to this
> effect:
>
> "Actually, the scale parameter is a ratio, and is doesn't have
> units. It just has its roots based on a pixels/meter constant."
>
> So, how is the scale parameter actually derived?
>
> - Matt
>
> --
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>

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