xml2struct is very slow...

13 views (last 30 days)
Robin Schäfer
Robin Schäfer on 5 Mar 2020
Commented: Anthony on 20 Nov 2023
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
  1 Comment
Robin Schäfer
Robin Schäfer on 17 Mar 2020
-UP-
I still need some speed improvement. Can anybody help?
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

Sign in to comment.

Answers (1)

Pierre Harouimi
Pierre Harouimi on 1 Dec 2021
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)
  1 Comment
Anthony
Anthony on 20 Nov 2023
Thank you, I missed this function when it was introduced and I was still using xml2struct.

Sign in to comment.

Categories

Find more on Programming in Help Center and File Exchange

Products


Release

R2019b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!