function [nedM] = Lla2Ned(lla1DegDegM,lla2DegDegM)

% [nedM] = Lla2Ned(lla1DegDegM,lla2DegDegM)
% function to difference latitude, longitude and altitude
% and provide an answer in NED coordinates in meters.
%
% Inputs: lla1DegDegM: mx3 matrix, [latitude(deg),longitude(deg),altitude(m)]
%         lla2DegDegM: mx3 or 1x3, [latitude(deg),longitude(deg),altitude(m)]
% Output: nedM =  lla1DegDegM - lla2DegDegM in NED coords (meters), 
%
% Useful rules of thumb for quick conversions: 
% 1e-5 (5th decimal place) of a degree of latitude approx= 1.1 meters
% 1e-5 of a degree of longitude approx= cos(latitude) * 1.1 meters

%Author: Frank van Diggelen
%Open Source code for processing Android GNSS Measurements

if nargin<2, error('Two inputs arguments needed'),end
[m1,n1]=size(lla1DegDegM);
[m2,n2]=size(lla2DegDegM);
if m2==1
  lla2DegDegM=ones(m1,1)*lla2DegDegM;
else
  if m1~=m2, 
   error('Second input must have one row or same number of rows as first input')
  end
end
if n1~=3 || n2~=3, error('Both input matrices must have 3 columns'),end

[xyz1M] = Lla2Xyz(lla1DegDegM);
[xyz2M] = Lla2Xyz(lla2DegDegM);
refXyz  = (xyz1M+xyz2M)/2;
[llaDegDegM] = Xyz2Lla(refXyz);
northM  = zeros(m1,1);
eastM   = zeros(m1,1);
for i=1:m1
    Ce2n = RotEcef2Ned(llaDegDegM(i,1),llaDegDegM(i,2));
    v = Ce2n*(xyz1M(i,:)-xyz2M(i,:))';
    northM(i)=v(1);
    eastM(i)=v(2);
end
downM = -lla1DegDegM(:,3)+lla2DegDegM(:,3);

nedM = [northM,eastM,downM];

end %end of function Lla2Ned
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Copyright 2016 Google Inc.
% 
% Licensed under the Apache License, Version 2.0 (the "License");
% you may not use this file except in compliance with the License.
% You may obtain a copy of the License at
% 
%     http://www.apache.org/licenses/LICENSE-2.0
% 
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS,
% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
% See the License for the specific language governing permissions and
% limitations under the License.