US Sectional Chart Updates for Salt Lake City and Las Vegas

On 5/22/2011 8:01 PM, 2KA wrote:
I've posted updated versions of the Salt Lake City and Las Vegas
charts on my website at http://www.soaringdata.info.

I do the whole batch of all the charts in the continental US once a
year, but (at least until I think of easier methods) it's too
expensive and time consuming to do them every charting cycle. If you
have a special need for a specific chart, feel free to email me
directly using the link on the site. I can probably accommodate some
special requests.

I've also done a bit of fine tuning in the way I do reprojections,
resulting in a little improvement in the sharpness of all the charts.

Happy Downloading!

Lynn Alley
"2KA"

When I opened your Twin Cities sectional in Geomapper, the image looks
like it is being view obliquely. The circles (compass roses around
VORs, etc) are elipses.

Why is that? What's the difference between the sectionals on your site
and the official sectionals you can download from the FAA for free?

--
Mike Schumann

Mike,

Sorry for taking something like four weeks to answer this. I won't
bore you with full explanation, but I just saw your message.

The quick answer to your question is that is how things look when you
view the lat/lon rectangular projection directly. My files really
aren't meant to be viewed in that way. Instead, they are intended as
input data for programs that require or prefer the rectangular
projection as the input format. The CMR versions are for seeYou, and I
use the TIFF versions mainly with Google Earth. If you follow the
instructions on my site for importing and viewing the sectionals into
Google Earth, you will see that the circles come out circular again.
Conversely, if you try to put a Mercator or Lambert projection into
Google Earth, the shapes get all distorted.

I'm not familiar with Geomapper. Do you mean Global Mapper? If so, try
setting Tools- Configure - Projection to something like Mercator. If
you do, you will see that the circles look normal.

There are two differences between my files and the ones you get straight
from the FAA. First, the FAA files are provided in the Lambert
Conformal Conic projection, which can't be used with programs like
SeeYou or Google Earth directly -- at least not with very good results.
Secondly, I trim off the edge material so that different sectionals
can be tiled together more or less seamlessly.

By the way, the FAA files are my source as well. I trim and reproject
them using a free package called FWTools.

For more information, study about the properties of different map
projections like Lambert, Mercator, etc.

Lynn Alley
"2KA"