Pablo's Mission Planning Website
Greetings Mission Planners,
For an interesting example of how you can stream data across the Internet (or SIPRNET) to a mapping client check out http://columbo.nrlssc.navy.mil/dmap/idx.jsp. There's an example "thick" client application (a program that runs on a PC like FalconView, ArcView or C2PC) and a "thin" JAVA client that runs inside a web browser. The real power of online data (think Weather, Threats and current Imagery) comes when it's combined with data already available on a local PC or LAN. I was able to pull up the image below showing the five sided house of pain combined with a street overlay:
For a better understanding of what motivates some people to write good software check out this story behind the Mac's Graphing Calculator:
NGA has posted the January/February Edition of Pathfinder, The Geospatial Intelligence (what, no hyphen?) Magazine. Highlights include an interview with Peter Teets, our acting Secretary of the Air Force. Must have been saving up news as this is a thick issue. There's also a good article about the Shuttle Radar Topography Mission (SRTM) DTED:
Unfortunately that plan will leave over half the SRTM cells with "voids". As discussed here, a void is a hole in the DTED without elevation data - meaning things like terrain masks and avoidance altitudes can't be calculated. Things will be even more interesting in aircraft that use DTED to calculate terrain following profiles. Recently I've been looking at elevation data in Western Washington. Here's an image of a TPC covering the area:
Now here's the SRTM Level 1 DTED:
Those black areas you see are data voids. McNeil Island (near the center of the image) and Squaxin Island (near the left edge) are completely covered by voids - in fact the voids match the outline of the islands. An ordinary, reasonable, prudent man ("ORP Man") would probably assume a data void totally surrounded by water would also be water. Unfortunately in this case the void regions contain islands with terrain extending up to 300ft and 250ft respectively.
If you're on automatic distribution for DTED you're likely sitting back expecting the SRTM Data to arrive in the mail. Unfortunately being on automatic distribution for "DTED" won't get you any "SRTM DTED" because it's treated as different product series by DLA. Also, DLA is not allowing any "Series All" distribution of SRTM DTED, so you'll have to get on distribution for each SRTM DVD. Best bite the bullet and do it sooner rather than later. The good news is with the data on DVD the number of discs you'll receive will be manageable.
The paragraph from Pathfinder, The Geospatial Intelligence Magazine talks about NGA's void fill program. If you get on automatic distribution for SRTM DTED you'd likely expect the void filled data. Unfortunately NGA is only distributing the void filled data on the NGA Gateway (SIPRNET and JWICS) and by special order. Of course if you download the data on a classified network then the data will be treated as classified, even though the SRTM data is either unclassified (Level 1) or limited distribution (Level 2). Best advise is to use the NGA Gateway to track what void filled data has been produced, then order the data you need. Hopefully NGA will update all the SRTM DVD's with the void filled data and distribute as an Edition 2 set.
From the MPUC Planning Committee:
Mission Planning Tip: Vertical Obstructions - Part 1
In the beginning there were charts, and the charts had obstructions. What's an obstruction? According to MIL-J-89100, the standard that defines the Joint Operational Graphic (JOG - 1:250K):
The 150ft obstruction threshold is unique to the JOG Charts - and only newer JOG charts include the 150ft obstructions. Both the Tactical Pilotage Charts (TPC's - 1:500K) and Operational Navigation Charts (ONC's - 1:1M) only include obstructions above 200 ft. Mil-O-89200 (ONC) says:
What about multiple obstructions in a congested area? While a 1:250K chart allows for a fairly "literal" obstruction display, a 1:1M chart just doesn't have enough space:
That means that on an ONC chart only the highest obstruction within a 9 square mile area is plotted. TPC's use a similar rule based on a 1 minute by 1 minute matrix. There's an exception to allow more obstructions in built up urban areas, but that still means a lot of obstructions can go unplotted.
How about the 1:50K Topographic Line Maps (TLMs)? Surprisingly enough, TLM's contain obstructions too:
Lets take a look at an example. The image below shows three towers located east of Destin Florida:
Because of the TLM's scale, it's safe to assume that the towers are plotted very close to their actual positions. To aid in tracking the tower position vs. what's displayed on a given chart I've placed a blue Local Point icon at the base of each tower. Remember, the tower's plotted location is determined by the dot at its base. Each tower also includes its MSL elevation and its AGL elevation - the AGL elevation is in parenthesis. At first glance the tower's elevations on the TLM seem low, but TLM's are designed for ground forces and the elevations are normally plotted in Meters - there are some TLM's with elevations in feet. Next comes NGA's Digital Orthorectified Imagery (DOI) from their Earth-Info website:
This imagery (available to the public to download) may appear similar to a limited distribution product provided by NGA, but any resemblance is purely coincidental. I've hidden the blue dots so you can see the ground. It's no surprise you can't see any sign of the towers. Even if the structures were visible there'd be no way to determine their height or style. Next comes the 1:250K JOG:
The JOG is a fairly literal representation of the actual tower locations, but the Northeastern most tower has been displaced to the east to avoid it's tower symbol overlapping the adjacent tower to the west. This demonstrates why you don't want to use plotted tower locations as precision radar targets - cartographers move stuff! Next up is the TPC:
The three separate towers on the JOG have been replaced with a single multiple tower symbol. Remember a TPC only plots the highest obstruction in a square mile area. Looking closely you can see the tower MSL/AGL elevations are substantially displaced to the Southeast. Someone flying could easily glance at their chart and mistake the elevations values to the west (237/223) for the elevations of the multiple towers - an error of nearly 200ft! What about the ONC?
The multiple tower symbol remains, but now it represents even more towers. You can also see how the airspace boundaries drawn on the TPC and ONC charts also hurts the legibility of the elevation text. Finally we get to the JNC:
Obstacles aren't a part of the JNC chart at all.
The examples above show how much influence the cartographer has on a chart's obstruction display. Three individual towers on a JOG become one multiple tower symbol on a TPC, and two multiple tower symbols on the TPC become a single multiple tower symbol on an ONC. An attempt to plot "all" the towers on the ONC would create an illegible chart, with towers piled up on top of each other. Unfortunately that's already happening across much of the US. Check out this section of ONC stretching from Birmingham to Talladega Alabama:
Good luck counting the number of towers, let alone reading all their elevations. The unfortunate reality is that the rapid growth in Cell Phone towers is making some charts (especially ONC's) unusable. A check of http://www.cellreception.com/ shows roughly 195 cell phone towers in Birmingham. For all the towers you see on a chart, there're even more that are unreported, unpainted and unlit.
Next time we'll begin discussing the Chart Update process, where obstruction data comes from and what it really tells you.