xml2struct is very slow...

Hello community,

I use xmlread() and xml2struct() to read latitude,longitude and time vector from an .gpx-file (which is formated as xml). This solution appears to be very, very slow. xml2struct >getNodeData takes over 90 % of the time of my whole script according to the profiler. Here is an example of the call in my function:

DOM=xmlread(file);
GPX=xml2struct(DOM);

time=strings(size(GPX.gpx.trk.trkseg.trkpt))';   % preallocation
lat=strings(size(time));
lon=strings(size(time));

for b=1:length(GPX.gpx.trk.trkseg.trkpt)     % extract parameters
    time(b)=GPX.gpx.trk.trkseg.trkpt{1,b}.time.Text;
    lat(b)=GPX.gpx.trk.trkseg.trkpt{1,b}.Attributes.lat;
    lon(b)=GPX.gpx.trk.trkseg.trkpt{1,b}.Attributes.lon;
end

lat=str2double(lat);
lon=str2double(lon);

time=extractAfter(time,'T');
time=extractBefore(time,'Z');

% the time will be formatted later on

The main problem on speed is not the for-loop but the xml2struct() command.

Here is an example of my data opened in texteditor:

<?xml version="1.0" encoding="UTF-8"?>

<gpx xmlns="http://www.topografix.com/GPX/1/1" version="1.1" creator="Polar Pro">

<metadata><author><name>Polar</name></author><time>2020-01-29T16:16:08.000Z</time></metadata>

<trk><trkseg>

<trkpt lat="-33.94066317" lon="18.86733817"><ele>0.0</ele><time>2020-01-29T16:16:10.000Z</time></trkpt>

<trkpt lat="-33.940 ….

Any suggestions to improve the speed? It does really matter, the function is going to be called several times...

EDIT 17.03.2020: Attached file as an example

[Robin Schäfer]

-UP-

I still need some speed improvement. Can anybody help?

Here is the link for xml2struct command: https://de.mathworks.com/matlabcentral/fileexchange/28518-xml2struct

I also tried to read data by this code, adapted from another question on this page. However, i ain't got it working for time and speed increase was not apparent...

DOM=xmlread(file);
x_root = DOM.getFirstChild;
trkpt_nodes = x_root.getElementsByTagName('trkpt');
time_nodes = x_root.getElementsByTagName('time');

lon=NaN(trkpt_nodes.getLength);
lat=NaN(size(lon));
time=NaN(size(lon));

for i = 0 : trkpt_nodes.getLength - 1
   trkpt_element = trkpt_nodes.item(i);
   lat(i+1)=trkpt_element.getAttribute('lat');
   lon(i+1)=trkpt_element.getAttribute('lon');
   % time extraction missing 
end

Answer 1

[Pierre Harouimi]

Long time after... But hope this will help

You can use the readstruct function (R2020b):

GPX     = readstruct("Example.xml");
time    = [GPX.trk.trkseg.trkpt.time]';
lat     = [GPX.trk.trkseg.trkpt.latAttribute]';
lon     = [GPX.trk.trkseg.trkpt.lonAttribute]';
time    = datetime(time,'InputFormat','yyyy-MM-dd''T''HH:mm:ss.SSS''Z');
[h,m,s] = hms(time);

Bonus: directly use the gpxread (Mappping Toolbox)

[Anthony]

Thank you, I missed this function when it was introduced and I was still using xml2struct.