How to Trim and Extend Lines / Polygons using QGIS and a bonus snapping vertex trick

[@samiseyhan2854]

it helped a lot, thx for sharing

[@antoniolocandro]

Glad it helped! I definitely struggled to use it until I understood the principles on it. I haven’t checked the current official documentation but may I should to see if it can be improved

[@studenttogermany]

Thanks for making this video. Its very helpful but for me it has given me half answer as far as my assignment is concerned. I want to have a query for whole work. Like from extending lines to the nearest line on the basis of one or two vertices. then converting those very new polygon shape into polygon. I have also done it manually but need command to do it automatically. Do you have any answer?

[@Pedro-944]

good video any one knows why the trim and extend often do so incorrectly? just as in the video you showed some instances of errors that where corrected once you changed CRS

[@antoniolocandro]

Most tools in QGIS only work correctly with a projected coordinate system (PCS), I suspect this is the case with the trim/extend tool.

[@moendopi5430]

@@antoniolocandro So I've been using this tool a lot for a while and I can't figure out how to chop off the dangles/overshoots. I do a lot of topological editing and the extend feature is really convenient. To trim I just use the vertex selecting tool and highlight the node of the overshoot and just delete it. I'm also working usually in NAD83 UTM 17N or 18N, so as to the projected system, it hasn't made a difference for me. I have found that snapping becomes a real issue if you have your project in one coordinate system and your data is in another or the wrong one (e.g. the project is in 18N but the geopackage for your lines was set to 17N.) Edit: Messing around a bit, I did get the trim tool to work, but I had to have a line that intersected the other without a node at their intersection. I usually run a smooth on my lines (for maps), then v.clean and fix geometries to take care of the majority of the topological errors. In the snapping tool bar I always keep toplogical editing turned on which will create a node when snapping a line to another. However, QGIS will see a dangle at that intersection until you split the line at that intersection. v.clean or fix geometries will usually either create a node at a dangle or split it, so the trim tool can't work on something like that.

[@MrPJBarney]

Thank you for this extremely helpful video. You are very knowledgeable with the software. May God, the Father of the Lord Jesus Christ, bless you.