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Aviation Forum / General / Soaring / November 2008A question for you GIS gurus out there
I am trying to parse ESRI shapefiles that describe FAA TFRs. But they are in NAD83 projections, with accompanying .prj files that look like this: PROJCS["North_America_Lambert_Conformal_Conic", GEOGCS["GCS_North_American_1983", DATUM["D_North_American_1983",SPHEROID["GRS_1980", 6378137.0,298.257222101]], PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]], PROJECTION["Lambert_Conformal_Conic"], PARAMETER["False_Easting",0.0], PARAMETER["False_Northing",0.0], PARAMETER["Central_Meridian",-93.13333333333335], PARAMETER["Standard_Parallel_1",47.41333914430852], PARAMETER["Standard_Parallel_2",47.43554955001912], PARAMETER["Latitude_Of_Origin",40.0],UNIT["Meter",1.0] ] A partial text dump of the corresponding .shp file looks like this: Shape:8 (Polygon) nVertices=37, nParts=1 Bounds:(-3703.999933,823435.273920, 0, 0) to ( 3703.999933,830843.274058, 0, 0) ( 0.00000000,830843.27405814, 0, 0) Ring (643.19289130,830787.00193647, 0, 0) (1266.84264658,830619.89536055, 0, 0) (1852.00012149,830347.03211620, 0, 0) (2380.88541892,829976.70258255, 0, 0) ... I have not been able to figure out how to use .prj parameters to transform the coordinates in the shapefiles to WGS84 (lat/lon) format. Seems to me it should be a rather simple formula. Anyone out there familiar with this problem? -ted/2NO Hi Ted, NIMA makes a freely available coordinate translator to do exactly what you are talking about. It's called GEOTRANS and they even release the source. It is available here: http://earth-info.nima.mil/GandG/geotrans/ -Mark > I am trying to parse ESRI shapefiles that describe FAA TFRs. But they > are in NAD83 projections, with accompanying .prj files that look like [quoted text clipped - 32 lines] > > -ted/2NO Mark, I've looked at GEOTRANS before, but it's packaged primarily as a GUI application, which doesn't help me. My processing will be done on a Linux server. GEOTRANS comes with source, but I haven't yet found the piece that does the transformation I'm looking for. Still looking though. -ted Hi; It is built & packaged for UNIX as well, see: http://earth-info.nima.mil/GandG/geotrans/#Downloading If that is no good, contact (GEOTRANS Project Managers) Brian Akers (St. Louis) and Dan Mullaney (Bethesda). In the final instant I might hve time to find the relevant functions but please try to investigate yourself. Thanks, Jonathan > Mark, I've looked at GEOTRANS before, but it's packaged primarily as a > GUI application, which doesn't help me. My processing will be done on [quoted text clipped - 4 lines] > > -ted >I am trying to parse ESRI shapefiles that describe FAA TFRs. But they >are in NAD83 projections, with accompanying .prj files that look like [quoted text clipped - 33 lines] >-ted/2NO >I'm no guru, I don't know the inner workings of the shapefile format, but I think I can be of some help. It appears to me that your data is in datum NAD83, projected in Lambert Conformal Conic. I'm guessing that converting from LCC to WGS84 is not a simple formula. The question is, what do you actually want done? Converting a list of points like waypoints or track log from LCC to WGS84 is easy, converting airspace features and outputting as a coordinate list is another. (Maybe it is easy and I just don't know how and someone else can fill you in) But I recommend converting formats of entire files or parts of files using conventional instruments like MapWindow, a free and quite capable GIS program. Among other things, it can buffer (add rings at selected distances) points, maybe that is all you need to do with that TFR file... With a $25 added application it will convert text file coordinates to google earth files too! That and the "GPS Converter" page people have mentioned here before gets my data from anything to just about anything else. http://www.gpsvisualizer.com/convert_input Global Mapper for $200 is the do it all converter. I have it too but I use MapWindow most of the time. If it's just a one time conversion and you have a specific output format, you could send me the data I can convert it for you. Thanks Jim but that doesn't help either ... anything interactive (GUI or otherwise) doesn't help; I need source code that I can compile in Linux and Windows (cygwin) environments... For the morbidly curious ... and with thanks also to those who responded by e-mail ... I found the answer to my question in a program available for both Windows and Linux by Gerald Evenden at the Woods Hole office of the Dept of the Interior, called "proj" (Cartographic Projection Procedures). The shapefile's .prj parameters indicate a geographic-to-geodetic Lambert Comforal Conic projection. Providing those parameters to the "proj" program with a request for inverse projection, along with all of the cartesian coordinates in the shapefile, yields the geocentric (lat/lon) coordinates. Armed with this weapon I can parse FAA TFRs (and state borders and anything else) into Special Use Airspace files. And thanks to Lynn Alley I also now know how to download a single .zip file with all of the TFRs already in geocentric format. Thanks 2KA! Not yet sure how useful it will be, but coming up soon, TFR airspace files. -ted/2NO > Not yet sure how useful it will be, but coming up soon, TFR airspace > files. TFRs are usually so short lived that it's unlikely anyone would have have current files loaded. What I think would be more useful for Arizona pilots is a depiction of the arrival and departure routes for KPHX and KTUS. Being close to cloudbase on a busy arrival route is unwise but how many pilots know where they are? Andy > > Not yet sure how useful it will be, but coming up soon, TFR airspace > > files. [quoted text clipped - 8 lines] > > Andy I disagree with you on TFRs (but the comments on approach/departure/ STAR etc. are right on. Those folks we might run into (we are likely to get the blame) just don't operate in our VFR world and we need to think how they think and where they will be). Given the danger (read mostly FAA enforcement danger) of violating a TFR and how little work it would be to load a file into a PDA I don't see the problem. Most TFRs (presidential, fire, etc.) are well known about the morning of a flight. Sure others might pop-up, but you'll get most this way. I published airspace files for Californian fire related TFRs (some that lasted weeks) for pilots flying out of Williams during summer. Sure at times you should not be anywhere near an active fire TFR, at other times there are large TFR areas with little activity and no smoke/visibility hazards. It literally is only a few clicks to synch such a file to a PDA. In very busy airspace/new TFR risk areas I'll bring along my Garmin 496 with XM weather and TFR alerts - it's helped with pop-up TFRs, and allowed me to radio other gliders to warn them. I subscribe to Ted's Just Soar airspace service and really appreciate what he is doing. Darryl > TFRs are usually so short lived that it's unlikely anyone would have > have current files loaded. I'm thinking more about contest situations. At Parowan this year we had TFRs in the task area most days. Having the PDA programmed to always load "dailytfrs.sua", even if the file is empty, would make for an easy daily procedure. The feature will be online before the next season starts. No subscription necessary; the server will auto-generate the SUA file each morning and pilots would just copy a fixed URL (e.g. http://www.justsoar.com/tfr/dailytfrs.sua) to their PDA. Advance thanks to Lynn Alley "2KA" for pointing me to the web resource with all the TFR shapefiles in one zip, and the tip on how to use wget to get it. ~ted/2NO >> TFRs are usually so short lived that it's unlikely anyone would have >> have current files loaded. [quoted text clipped - 3 lines] > always load "dailytfrs.sua", even if the file is empty, would make for > an easy daily procedure. I'll like that feature during our fire season, when we might have 10 or more fire TFRs within reach (WA, OR, ID) in a bad year.  SignatureEric Greenwell - Washington State, USA * Change "netto" to "net" to email me directly * Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4 * New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more * "A Guide to Self-launching Sailplane Operation" at www.motorglider.org I use a Garmin 396 with XM weather. It's $50 a month for the weather service. Displays TFR's, and all manner of weather data including lightning strikes and winds aloft. bumper >>> TFRs are usually so short lived that it's unlikely anyone would have >>> have current files loaded. [quoted text clipped - 6 lines] > I'll like that feature during our fire season, when we might have 10 or > more fire TFRs within reach (WA, OR, ID) in a bad year. |
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