[Xastir] Re: Bounding boxes

[Gerry Creager N5JXS]

DRGs are also processed so that they can be, with an appropriate GIS 
package (as defined by that government agency ESRI, but I digress) 
seamlessly tiled.

Tom Russo wrote:
> On Mon, Oct 13, 2003 at 09:04:57PM -0700, a Mr. Richard Feyler of Fort Lee, New Jersey <archer at eskimo.com> writes 'Dear Rosanne Rosannadanna':
> 
>>On Mon, 13 Oct 2003, Tom Russo wrote:
>>
>>
>>>Um... since the geotiff files are originally scanned from paper maps
>>>that are lat/lon rectangles, and small ones at that, isn't it usually
>>>the case that the transformation is mostly a rotation, and not much of
>>>a stretching operation?
>>
>>No.  You're thinking of the paper USGS maps that you buy.  Take a
>>look at one of the DRG files in a normal TIFF viewer.  They have been
>>distorted into a UTM projection.  
> 
> 
> Actually,  I think the paper maps *are* distorted, too --- they are UTM 
> projections of a 7.5' lat/lon band, and that's what the collar info
> even says.  I'm looking at a USGS paper quad right now, and seeing in the 
> bottom left corner that it states "Projection and blue 1000-meter ticks: 
> Universal Transverse Mercator."  It's not just the DRGs that have been
> projected into UTM, it's the original source map.
> 
> You're right, of course, the DRGs are distorted, and I'm just too used to 
> looking at maps from the area I'm in, where the quads are still *roughly* 
> rectangular.  Go farther north than where I live and these effects are more 
> noticable.
> 
> I believe that the only real difference between the paper maps and the 
> DRGs is that they've been rotated  --- the paper maps are made so the 
> N/S neatlines are as parallel to the edge of the paper as they can be,
> whereas the DRGs are rotated so the UTM grid is parallel to the pixel grid.
>