Hi Gavin, Create the second CSV file with only one row (the latest one).
Rémi 2014-03-11 9:34 GMT+01:00 Gavin Macaulay <[email protected]>: > Bob, > > Thanks for the suggestion. How does one get the csv provider to read just > the first line? > > Gavin > > > On 10/03/2014 10:25 p.m., Basques, Bob (CI-StPaul) wrote: > >> Gavin, >> >> Set up the CSV file creation to append to the top of the file instead of >> the bottom, then just read the first line for the special cartography. >> >> If you are running on Linux, there are a whole bunch of options with >> AWK/GREP, etc to get the data outputting in a more favorable fashion for >> reading. >> >> My first thought was to suggest the SQL path though, this gives you lots >> of options for archiving and looking at the path/trail over time . . . >> >> I've just completed doing something similar for a AVL tracking system. >> >> Bobb >> >> >> >> -----Original Message----- >> From: [email protected] [mailto:qgis-user-bounces@ >> lists.osgeo.org] On Behalf Of Gavin Macaulay >> Sent: Monday, March 10, 2014 3:18 PM >> To: [email protected] >> Subject: [Qgis-user] Labelling expressions: how to select the 'last' row >> in a csv dataset >> >> Hi, >> >> I have a csv file that looks like this: >> >> datetime, latitude, longitude, speed >> 2014-03-07T06:11:56.794000, 69.6930, 19.0321, 0.0 >> 2014-03-07T06:12:56.791000, 69.6904, 19.0291, 10.0 >> 2014-03-07T06:13:56.787000, 69.6879, 19.0257, 10.0 >> >> A new row gets added to the file every second or so. I load this file >> into QGIS as a csv file with the watch option turned on so that every time >> the map is refreshed, the map plots any new points that have been added to >> the file. >> >> I would like to have the most recent line in the file plotted with a >> different symbol to the rest (the data represents realtime data from a >> moving ship so it's good to highlight the latest position). I can almost do >> this using the expression based labelling, but not quite (I can get a row >> number, but not the total number of rows, so can't do something obvious >> like: $rownum == $numrows, or $id == max($id)). >> >> Any suggestions on how I can achieve this? I could move the data into a >> SQL-based layer and choose the last row using an SQL statement, but the >> simplicity of generating the csv files is attractive. >> >> Thanks >> >> Gavin >> _______________________________________________ >> Qgis-user mailing list >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/qgis-user >> >> >> > _______________________________________________ > Qgis-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/qgis-user >
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