I am quite new to QGIS, so sorry about maybe to simple question.

I would like to set the GPS track line width in map units (meters). I use QGIS in hydrographic survey in a boat. Having the track line in map units, I could see if I have covered the survey area totally. Like if I have "painted" the survey area. Now the line width is in pixels (px).

So, is this possible to do by adjusting the setting or is there an "easy" way to do it? Doing this after survey is of course possible, but I would like to it in the boat.

  • Could you describe your "in situ" setup? – Erik Apr 24 '20 at 13:41
  • Use the buffering tool in QGIS to create a polygon at your desired distance from your GPS track line. See this link: docs.qgis.org/2.8/en/docs/gentle_gis_introduction/… – GBG Apr 24 '20 at 15:47
  • I have a tablet (win10) with GPS and an echosounder attached to it. I use the QGIS to navigate through my survey path by looking my location and steering the boat. The swath (survey width) of echosounder is typically 3 - 20 metres. I try to cover the survey are in an optimal way, without blank areas and double work. – jamia Apr 27 '20 at 10:54
  • Buffering is possible but I think it can be done only afterwards? I need a real time line drawing to steer my boat. – jamia Apr 27 '20 at 10:56

If I understood you well, you go up and down in a kind of grid with your boat and have a certain width to the left and right of your boat that you consider to be "covered area" - let's say a band with 5.5. meters width.

You can easily change the width of your line in either "map units" or "meters in scale". I defined a line-layer in EPSG 4326 (that's what you use for GPS, aren't you?) and set the project EPSG to 3857 (projected CRS with units=meters) or whatever is suitable for your area. If you have EPSG 4326 as project EPSG, than you can't use "map units" for line-width (since it's in degree). However, "meters" should still work.

Mark the line-layer, open layer styling, select the line and change the units from pixels to "map units" or meters - see screenshot. I defined a 5.5 meters width and selected a red, semi-transparent color: if the boat goes up and down in a 5-meter distance grid, you have overlapping portions (dark red stripes). Only for visualisation purpose, I added the thin black lines in 5 meter-distance to show the boat's route. enter image description here

  • Thank you for your answer. I am using EPSG 3067 at survey. GPS data is originally 4326. And yes, I am driving a grid pattern in a survey. I tried to do according to your answer. Layer styling could work if the GPS track is a layer. The GPS track is logged only in nmea format and QGIS is not accepting nmea format as a layer. And also the log is written in real time and I suppose the log file is then "open". I don't know if QGIS can read an "open file". I really need a real time track line drawing so I can follow my survey grid pattern to avoid "empty areas" and double work. – jamia Apr 27 '20 at 10:21

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