At 23:45 17 November 2008, Tuno wrote:
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
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.