Split polylines at a specific distance in QGIS / ogr2ogr

Question

Similar to this question I have a set of polylines that I need to be split by a equal distance. How do I do this with QGIS, gdal/ogr2ogr and other open source tools (on Mac)? I don't have access to ArcGIS, therefore not a duplicate question, I hope.

I figured out to extract the coordinates at a specific distance from start of a line with this in QGIS (1000 m from start):

 x(line_interpolate_point($geometry, 1000))
 y(line_interpolate_point($geometry, 1000))

From there I'm not sure how to continue.

I need this to be able to create points along contour lines where I can extract angle and elevation value (from attribute). See this question and answer where I need this information.

Is your question specific to ogr2ogr solution? If you like there is v.split.length tool in QGIS Processing Toolbox. — Kazuhito, Oct 11 '17 at 23:39
Possible duplicate of Split multiple polylines by distance in ArcGIS — ahmadhanb, Oct 12 '17 at 03:00
The solution to the above duplicate question is done using QGIS and GRASS — ahmadhanb, Oct 12 '17 at 03:02
@ahmadhanb if it is not too much trouble, will you be able to post your solution as answer to this? Given the linked op was meant for ArcGIS, I feel this question looks most apt to... — Kazuhito, Oct 12 '17 at 04:24
@Kazuhito thank you very much for your suggestion. I posted as an answer — ahmadhanb, Oct 12 '17 at 04:36
The answer in https://gis.stackexchange.com/questions/201955/split-multiple-polylines-by-distance-in-arcgis is indeed duplicate but the question has no tag for QGIS and therefore QGIS users may not find it. Would it be better to keep this question open or edit the tags and perhaps title of the other question? — user30184, Oct 12 '17 at 13:04

ahmadhanb · Accepted Answer · 2017-10-12T08:19:16.060

2

There is a GRASS plugin under QGIS to split the polyline by specific length. The tool "v.split.length - Split lines to shorter segments by length" does exactly what you are asking for, as you can see below:

Under the Maximum segment length, you need to specify the desired length. In this example it is specified every 500 meters.

Before split:

After applying split tool:

You need to make sure that your data is projected to a suitable spatial reference that uses meters or feet. However, it may not give the desired length if the lines are complex or have some topological errors.

edited Oct 12 '17 at 08:19

answered Oct 12 '17 at 04:35

ahmadhanb

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I read here that it doesn't really do it the right way? – oskarlin Oct 12 '17 at 07:35
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@OskarKarlin I updated my answer with illustration. However, sometimes the results cannot be as desired due to topological errors in the input file or using unprojected data. – ahmadhanb Oct 12 '17 at 08:20
OK, then I'm satisfied! – oskarlin Oct 12 '17 at 16:58

Split polylines at a specific distance in QGIS / ogr2ogr

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