[Xastir] Re: USGS DRG files no longer free.. (Tyler Allison)

[Curt Mills, WE7U]

On Mon, 6 Oct 2003, Tyler Allison wrote:

> True. That's what I get.
>
> Im not trying to be a tard really. I just dont see how 121.20692W turns
> into -121. Shouldnt the line be -121.20692 or can you simply drop the
> decimal section when building a fdg file from hand?

Sorry.  W = -
        E = +
        S = -
        N = +

So 121.20692W = -121.20692


> How do I know which number to use as the east/south/west/north boundaries?
> The listgeo file has two numbers listed for things like 'lower left' or
> 'upper right' which obviously isnt east or south ;)

Pick the average?


> Right now Im just sorta looking at the 'working' geotif files and saying...
>
> Well the second number on the third line of that listgeo was a 121 and the
> fdg for east boundary is 121 so I must need to take the third line of my
> listgeo output and make it my east boundary.  I have no idea what it all
> means Im just faking it ;)  I'd prefer to understand what Im doing instead
> of "take the third number, drop the decimal and make it the East boundary"

The problem is that the projection used for the USGS DRG maps is the
UTM projection.  We're not using that in Xastir.  I'd take the
average of the values and that'll get you so close you won't care.
So, for the two west values, average them.  Same for the two north
values, the two south values, and the two east values.  That'll give
you four values to use for the boundaries.

-- 
Curt Mills, WE7U                    hacker_NO_SPAM_ at tc.fluke.com
Senior Methods Engineer/SysAdmin
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