A Free Source for US Airspace Data

Last December I reported in this forum that I was starting a project
to extract airspace information from the National Airspace Resource
Files (NASR) published by the National Flight Data Center, and to
translate that information into file formats commonly used in the
sport aviation community (such as OpenAir .txt and Tim Newport-
Peace .sua formats). I embarked on this effort because of the
withdrawal from publication of the Digital Aviation Flight Information
File (DAFIF), which for years had been the main free source of
airspace data used by US sport aviators.

I am pleased to announce that this project has finally come to
fruition. I anticipate that there might be some questions about it,
so I am taking the opportunity in advance to answer some of them here.

Question 1:

How does this data compare to translations based on the National
Flight Database (NFD), such as those available by subscription on the
JustSoar website?

Answer:

The arcs and lines that make up airspace boundaries are specified
explicitly in the NFD data. By contrast, the NASR data comprises only
lists of points along the airspace boundaries. It is, however,
possible from those lists to compute estimations of actual boundary
positions by fitting arcs and lines to them. In my translation the
computation is done such that the estimated boundary lies within about
300 ft. (.05 NM) of the points given in the NASR data. This is the
expected error of the translation process.

The question of the accuracy of the NASR data itself deserves some
comment. The FAA recently initiated a project to publish and re-
verify airspace data in the NASR using a new file format (GIS
shapefiles). In July, this project was completed for airspace classes
B, C, and D, and the “not for navigation” designation that had
previously been applied to those shapefiles was removed.

The shapefile project for special use airspace, including Restricted
and Prohibited airspace, Alert Areas, and MOAs, is just getting
started.. SUA data is currently published in the NASR using an older,
much less precise format that has been in use for years. I have
found, corrected, and reported the most obvious errors in the SUA
data. Some of these have been as much as a mile or so.

Generally speaking, I think the NASR data compares favorably to the
old DAFIF files, although there may be some exceptions.

Question 2:

Why use the NASR data at all? Isn’t the NFD data adequate?

Answer:

Unlike the NFD data, the NASR subscription is free of charge, and
comes without a restrictive license agreement. My translations are
also free of charge, and may be freely copied and redistributed.

Question 3:

Where can I get your translations made from the NASR files?

Answer:

The files for the next charting cycle, effective September 25, are now
available in the Special Use Airspace section of the Worldwide
Turnpoint Exchange.


Lynn Alley
“2KA”


PS for programmers: I have made the source code for the programs that
produce the NASR translations freely available in a public domain
SourceForge project called “Air2”, in the SVN repository. You may use
it for any purpose you wish. Obtaining and installing the required
libraries and languages is fairly involved, and shouldn’t be
undertaken casually. Expect to spend days.

On Sep 7, 11:18*am, 2KA wrote:
Last December I reported in this forum that I was starting a project
to extract airspace information from the National Airspace Resource
Files (NASR) published by the National Flight Data Center, and to
translate that information into file formats commonly used in the
sport aviation community (such as OpenAir .txt and Tim Newport-
Peace .sua formats). *I embarked on this effort because of the
withdrawal from publication of the Digital Aviation Flight Information
File (DAFIF), which for years had been the main free source of
airspace data used by US sport aviators.

I am pleased to announce that this project has finally come to
fruition. *I anticipate that there might be some questions about it,
so I am taking the opportunity in advance to answer some of them here.

Question 1:

*How does this data compare to translations based on the National
Flight Database (NFD), such as those available by subscription on the
JustSoar website?

Answer:

The arcs and lines that make up airspace boundaries are specified
explicitly in the NFD data. *By contrast, the NASR data comprises only
lists of points along the airspace boundaries. *It is, however,
possible from those lists to compute estimations of actual boundary
positions by fitting arcs and lines to them. *In my translation the
computation is done such that the estimated boundary lies within about
300 ft. (.05 NM) of the points given in the NASR data. *This is the
expected error of the translation process.

The question of the accuracy of the NASR data itself deserves some
comment. *The FAA recently initiated a project to publish and re-
verify airspace data in the NASR using a new file format (GIS
shapefiles). *In July, this project was completed for airspace classes
B, C, and D, and the “not for navigation” designation that had
previously been applied to those shapefiles was removed.

The shapefile project for special use airspace, including Restricted
and Prohibited airspace, Alert Areas, and MOAs, is just getting
started.. *SUA data is currently published in the NASR using an older,
much less precise format that has been in use for years. *I have
found, corrected, and reported the most obvious errors in the SUA
data. *Some of these have been as much as a mile or so.

Generally speaking, I think the NASR data compares favorably to the
old DAFIF files, although there may be some exceptions.

Question 2:

Why use the NASR data at all? *Isn’t the NFD data adequate?

Answer:

Unlike the NFD data, the NASR subscription is free of charge, and
comes without a restrictive license agreement. *My translations are
also free of charge, and may be freely copied and redistributed.

Question 3:

Where can I get your translations made from the NASR files?

Answer:

The files for the next charting cycle, effective September 25, are now
available in the Special Use Airspace section of the Worldwide
Turnpoint Exchange.

Lynn Alley
“2KA”

PS for programmers: *I have made the source code for the programs that
produce the NASR translations freely available in a public domain
SourceForge project called “Air2”, in the SVN repository. *You may use
it for any purpose you wish. *Obtaining and installing the required
libraries and languages is fairly involved, and shouldn’t be
undertaken casually. *Expect to spend days.

Lynn - Thanks for this undertaking - I understand how much work
was involved, and we will all benefit.
Sincere Thanks,
Best Regards, Dave "YO electric"

PS: Do you expect a "reasonably smooth, royalty-free, transition"
as the FAA publishes all SUA in GIS format and eliminates the
legacy format ?

I would really hesitate to speak authoritatively for the FAA. My
expectation, however, is that they will simply add the GIS format for
the SUAs to the NASR subscription. Eventually, I would expect them to
eliminate the older text-based format. I would be highly surprised if
they started talking about a royalty. There has never been any such
thing for the NASR data.

L.

I don't want to discourage anyone from using Lynn's airspace files,
but I do want to encourage pilots to understand the data they're
using, and in this case the TINSTAFL rule applies (along with its
corollary, YGWYPF).

I took a quick peak at the current version of Lynn's NASR translation
at the turnpoint exchange, and looking at just the Phoenix area, I
could find differences from the current (justsoar.com) NFD version.
For example, the Luke AFB Class D in Lynn's file is the old 4.4 mile
radius (it was changed to 5.6 miles in May of 2007, along with a
couple of other tweaks). Now, if you were a contest manager and had to
designate a particular data set for your contest, which would you
choose?

(Speaking of contests, I've arranged with the Contest Committee to
provide current airspace files for all sanctioned contests, for free
distribution among the pilots for use at that contest.)

A general difference, which may or may not be significant depending on
how picky you are about the different flavors of SUA, is that all of
the MOA and ALERT areas in Lynn’s version are categorized as “DANGER”..
Danger is a valid SUA type, but has a different definition than MOA or
ALERT.

Something Lynn’s data does have that I wish the NFD had is effective
times for the MOAs. But the NACO has told me it’s on the list of
things they’re adding to the NFD, along with contact frequencies. If
NACO hasn't added these by 2009, I plan on adding them myself by cross-
referencing other available data.

A significant item missing from both data sets are USA boundary data
-- pilots flying close to Mexico or Canada need to rely on something
besides their airspace data to stay legal. (Yes, that's coming soon as
a justsoar.com add-on too

~ted
ASG28.7 "2NO"

ps I cannot find anything anywhere in the faa.gov or naco.faa.gov web
sites that discusses publishing SUA in GIS format. I'm not saying it's
not there -- I just can't find it.

pps it's also worth noting that the NFD, as the FAA/NACO's designated
source for in-flight digital airspace navigation data, is updated
every 28 days. These updates are not just routine changes to airspace
definitions -- they include the addition of things like corridors
through restricted areas, special case airspaces (e.g. the Grand
Canyon no-fly zone, which is only in the NFD), and (coming soon)
contact frequencies.

This off-season the justsoar.com site will also add a few optional
features, including country boundary data and a subscriber-populated
database of landout locations. Stay tuned ...