FGFS-4.1/gr-air-modes
4
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Temp commit before I rip out the relative stuff

Browse Source
This commit is contained in:
Nick Foster 2012-12-07 09:36:16 -08:00
parent 1f0ef143a0
commit 017cce7ec4
1 changed files with 14 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

34
python/mlat.py
View File

@ -105,7 +105,7 @@ def mlat_iter(rel_stations, prange_obs, guess = [0,0,0], limit = 20, maxrounds =
prange_est = [[numpy.linalg.norm(station - guess)] for station in rel_stations]
#get the difference d_p^ between the observed and calculated pseudoranges
dphat = prange_obs - prange_est
#create a matrix of partial differentials to find the slope of the error in X,Y,Z directions
#create a matrix of partial differentials to find the slope of the error in X,Y,Z,t directions
H = numpy.array([(numpy.array(-rel_stations[row,:])+guess) / prange_est[row] for row in range(len(rel_stations))])
H = numpy.append(H, numpy.ones(len(prange_obs)).reshape(len(prange_obs),1), axis=1)
print "H: ", H
@ -120,19 +120,20 @@ def mlat_iter(rel_stations, prange_obs, guess = [0,0,0], limit = 20, maxrounds =
return guess
#gets the emulated Arne Saknussemm Memorial Radio Station report
#here we calc the estimated pseudorange to the center of the earth, using station[0] as a reference point for the geoid
#here we calc the estimated pseudorange to the center of the earth, using station[0] as a reference point
#in other words, we say "if the aircraft were directly overhead of me, this is the pseudorange to the center of the earth"
#if the dang earth were actually round this wouldn't be an issue
#this lets us use the altitude of the mode S reply as info to construct an additional reporting station
#i haven't really thought about it but I think the geometry (re: *DOP) of this "station" is pretty lousy
#but it lets us solve with 3 stations
def get_fake_station(surface_position, altitude):
return [numpy.linalg.norm(llh2ecef((surface_position[0], surface_position[1], altitude)))] #use ECEF not geoid since alt is MSL not GPS
def get_fake_prange(surface_position, altitude):
fake_xyz = numpy.array(llh2ecef((surface_position[0], surface_position[1], altitude)))
return [numpy.linalg.norm(fake_xyz)] #use ECEF not geoid since alt is MSL not GPS
#func mlat:
#uses a modified GPS pseudorange solver to locate aircraft by multilateration.
#replies is a list of reports, in ([lat, lon, alt], timestamp) format
#altitude is the barometric altitude of the aircraft as returned by the aircraft
#altitude is the barometric altitude of the aircraft as returned by the aircraft, if any
#returns the estimated position of the aircraft in (lat, lon, alt) geoid-corrected WGS84.
#let's make it take a list of tuples so we can sort by them
def mlat(replies, altitude):
@ -142,31 +143,26 @@ def mlat(replies, altitude):
timestamps = [sorted_reply[1] for sorted_reply in sorted_replies]
nearest_llh = stations[0]
nearest_xyz = llh2geoid(stations[0])
nearest_xyz = numpy.array(llh2geoid(stations[0]))
#list of stations in XYZ relative to the closest station
rel_stations = [numpy.array(llh2geoid(station)) - numpy.array(nearest_xyz) for station in stations[1:]]
rel_stations = [numpy.array(llh2geoid(station)) - nearest_xyz for station in stations[1:]]
#add in a center-of-the-earth station if we have altitude
if altitude is not None:
rel_stations.append([0,0,0] - numpy.array(nearest_xyz))
rel_stations.append([0,0,0] - nearest_xyz)
rel_stations = numpy.array(rel_stations) #convert list of arrays to 2d array
#get TDOA relative to station 0, multiply by c to get pseudorange
prange_obs = [[c*(stamp-timestamps[0])] for stamp in timestamps[1:]]
print "Initial pranges: ", prange_obs
if altitude is not None:
prange_obs.append(get_fake_station(stations[0], altitude))
altguess = altitude
else:
altguess = nearest_llh[2]
prange_obs.append(get_fake_prange(nearest_llh, altitude))
print "Initial pranges: ", prange_obs
prange_obs = numpy.array(prange_obs)
#initial guess is atop nearest station
#xguess = numpy.array(llh2ecef([nearest_llh[0], nearest_llh[1], altguess])) - numpy.array(nearest_xyz)
xyzpos = mlat_iter(rel_stations, prange_obs)
llhpos = ecef2llh(xyzpos+nearest_xyz)
@ -191,11 +187,7 @@ if __name__ == '__main__':
testalt = 8000
testplane = numpy.array(llh2ecef([37.617175,-122.400843, testalt]))
testme = llh2geoid(teststations[0])
teststamps = [10 + numpy.linalg.norm(testplane-numpy.array(llh2geoid(teststations[0]))) / c,
10 + numpy.linalg.norm(testplane-numpy.array(llh2geoid(teststations[1]))) / c,
10 + numpy.linalg.norm(testplane-numpy.array(llh2geoid(teststations[2]))) / c,
10 + numpy.linalg.norm(testplane-numpy.array(llh2geoid(teststations[3]))) / c,
]
teststamps = [10+numpy.linalg.norm(testplane-numpy.array(llh2geoid(station))) / c for station in teststations]
print "Actual pranges: ", sorted([numpy.linalg.norm(testplane - numpy.array(llh2geoid(station))) for station in teststations])