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Greetings Mission Planners,

An error has been found with the Camp A.P. Hill Military Installation Map (MIM) on the CONUS MIM edition 4 CD:

The 9 CADRG MIM frame files have a 1000 meter registration error.  The error will be fixed on a subsequent CD but until then you should delete those frames!  Fortunately there's 1:50K chart coverage (without the MIM overprint) that you can use.  The MIM covers R6608 and Quantico's Drop Zones.

Recently you may have received a Confidential NGA CD.  Confidential is a security classification just like Secret or TS and the data needs to be protected appropriately, i.e. you can't put the data onto an unclassified machine.  Since there aren't any Confidential PC's (that I've ever seen)  you'll have to protect the data as if it were Secret.

The Air Force's Geospatial Information and Services (GI&S) regulation 14-205 has been re-released and is available here.  14-205 is our bible for geospatial data and explains who is responsible to get you the data you need to plan and conduct operations effectively.  It doesn't compare with a Steven King page turner, but  if you're in the AF and deal with geospatial stuff then you need to have a copy on your hard drive and be familiar with the information.

Mission Planning Tip: Digital Terrain Elevation Data (DTED) Part I

DTED is the oldest digital mapping format that we still use today.  Although lost in the sands of time, DTED was originally developed to drive 3D milling machines and provide elevation data needed for cruise missile planning.  The DTED format hasn't kept pace with more modern formats, but since so many systems have been developed to use the existing DTED spec it's very difficult to make changes.  The formal DTED specification is MIL-PRF 89020B, dated 23 May 2000.  When in doubt, the PRF rules.  DTED comes in several varieties, but right now the only formats defined by formal specification are DTED 0, DTED 1 and DTED 2.  Shuttle Radar Topography Mission (STRM) DTED was collected and processed in a unique fashion (more about that later) but follows the same specification as plain old "classic" DTED.

A DTED file is a matrix of elevation values for a one degree by one degree area.  From the equator to 50 N/S DTED 0 has a grid spacing of 30 seconds, DTED 1 has a grid spacing of 3 seconds and DTED 2 has a grid spacing of 1 second.  You'll sometimes here DTED 1 referred to as "3 arc second" DTED and DTED 2 referred to as "1 arc second" DTED.  FalconView uses these terms in the status bar when you're viewing the DTED map.  Because of the greater density, a DTED 1 file is 100 times the size of a DTED 0 file and a DTED 2 file is 9 times the size of a DTED 1 file.  DTED files aren't compressed so a file of empty ocean is just as large as one in the middle of one in the Rocky Mountains.  DTED 0 is unique because in addition to the normal elevation file there are files containing the average, maximum and minimum elevation for 3 degree by 3 degree boxes centered on each DTED post.  The Max/Min/Avg values are calculated using  DTED 1 data.  FalconView doesn't support DTED 0 so this is only a curiosity.

A DTED file consists of elevation values at that point only!  There is no attempt to capture the highest terrain elevation.  The elevation value is stored in meters and referenced to MSL.  Normal DTED values are for the "bare earth" and don't reflect the elevation of manmade structures or vegetation.  

DTED 1 has 30 second spacing, but what does that really mean?  The image below shows a DTED 1 grid on Shea Stadium:

The spacing of DTED 1 points is roughly akin to the distance from home plate to the foul pole.  Terrain that can fit inside the boundaries of a baseball field could be missed in DTED 1.  The next picture shows a DTED 2 grid on top of Shea Stadium:

Not surprisingly, there's a lot more dots.  The red dots are included in DTED 1 and DTED 2 files and the values they return from either file should be identical because they reflect the elevation at that point only!  The spacing of DTED 2 is roughly equal to the distance from home plate to first base.  Terrain that can fit within a baseball diamond might be missed with DTED 2.  

Interestingly enough, all classic DTED is Limited Distribution so I can't use it in this newsletter.  Instead I used the USGS National Elevation Database (NED) downloaded from the USGS National Map Seamless Data System.  I then used MICRODEM to convert the data to the military DTED 1 and DTED 2 formats (nobody uses the DTED format except for NGA and other Military producers). MICRODEM is written by Professor Peter Guth at the US Naval Academy.  It's a great tool for doing advanced geospatial stuff - and it's free!

Today's example is Sunrise Mountain, near Nellis AFB:

This is the way Sunrise Mountain looks with a DTED 1 grid:

I'm not going to bother showing the Level 2 grid because all it looks like is a bunch of dots.  FalconView 3.3 and beyond can generate contours which is a great way to visualize the DTED.  This is how Sunrise Mountain's contours look based on Level 1 data:

The contour interval is 40 ft and the highest elevation contour is 3320 ft.  This is how the Level 2 Contours look:

The contours have a lot more detail, but the highest contour is still 3320 ft.  Lets zoom in on the highest part of Sunrise Mountain.  These are the Level 1 contours:

And this is Level 2 - this time with the DTED grid displayed:

Next I'll zoom all the way in on the highest elevation values and switch to a 10ft contour interval.  First DTED 1:

Now Level 2:

You can see how the DTED 1 grid misses the very highest terrain.  The maximum DTED 1 elevation is 3333 ft and the maximum DTED 2 elevation is 3360 ft.  The USGS 1:24K map shows the peak elevation of 3364, so neither is too far off.  Next lets look at the mountain in 3D in SkyView.  First using DTED 1:

Next here's Sunrise Mountain using Level 2 Data:

Should you be using DTED 1 or DTED 2?  Well if you want the absolute highest elevations and most detailed terrain then use DTED 2.  Unfortunately FalconView 3.2 doesn't really use DTED 2 for very much at all (the first DTED 2 functionality was going to be in 3.3 but part was done early).  If DTED 2 is available FalconView will use it to determine the running elevation underneath your cursor, but that's about it.  Subsequent versions of FalconView and SkyView can use it for more and more things. 

In the above images you may have noticed that the N/S and E/W spacing isn't identical:

Because DTED spacing is based on arc seconds the E/W distance gets squashed as you move North.  Eventually the DTED specification adjusts the spacing at 50N/S and again at 70N/S, 75N/S and 80N/S. 

Next time I'll talk about how accurate DTED is, what metadata is available (that FalconView can't display) and provide an example of "DTED Gone Bad."

Paul