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Trimming many lines to a polygon - best practices for vicinity maps, isolating topography, etc...

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I just downloaded some GIS data for a client's project.  It's a huge file with lots of data well outside the bounds of the project vicinity and must be reduced in content and size to be usable.  How would you trim the contours inside a boundary, such as the image below?  Keep in mind, this dataset is huge an has 1000s of contours within the subject area unlike this example image:




My approach thusfar....

Delete all polylines outside of the project area.

Attempted to "trim" the remaining lines that cross the subject area using Trim, Connect/Combine, and Clip Surface and the rectangle defining the subject area.  This results in a no warning insta-crash within Vectorworks.

Draw a line to trim individual contours to.  This works but is extremely time consuming in number of contours and amount of time VWX requires to trim these 2D contours.... 8 minutes to execute a single trim on a single object!

The dataset is too big to turn into a site model and crop, crashes.


Thanks for any ideas.

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Posted (edited)
6 hours ago, markdd said:

Have you tried the very underused Trim menu command?


I had not tried the menu version of trim.  It has been running for over an hour now processing all of the contours and we shall see if it works 🙂  Thanks for the suggestions.

*** Update.  After 6 hours of beachball theatrics and pinning my RAM, it actually trimmed the whole mess correctly.  Thanks again @markdd!

Edited by jeff prince
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5 hours ago, zoomer said:




I am cleaning up large IFC imports in Bricscad.

The main File is already running since 9 days now ....

Wowzer! 9 days??? Thats the meaning of patience.  Hope its on a separate computer so you can work on other things. 

I have tried the Split tool which works ok. But not on huge data sets. Needs a separate split for each edge



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8 hours ago, Benson Shaw said:

Hope its on a separate computer so you can work on other things. 


Yes, it's on the PC.

And I opened a second instance of Bricscad for smaller files.

But have to wait there too.

If I had more than 64 GB RAM, I could open more instances,

the 3950X would most times have still enough idling cores left.


VW jobs work mostly ok and fluid with these huge files on my M1 Mini.

Bricscad seems to need the PC, but has better Tools for cleaning up

geometry of those crappy IFC or Revit files available.

Like Simplify Solids and all kind of Audit options to fix broken geometry.

Or purging of same Symbols that are used by a single instance.


Once cleaned up they will come back into VW.

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On 7/25/2021 at 9:45 PM, unearthed said:

@unearthed!  Good one! This old dog forgot the trick. Thanks for reminding.


@jeffprince    Give it a whirl - In QGIS, it's called a clip or clipping layer.  Similar to a vwx SLVP crop, or a site model crop.  Advantage here is that the result is a new shapefile layer which can then be exported as a shapefile containing only the clipped geometry with associated georef and other data.  Import of clipped shapefile into vwx is solid.  Loads of tutorials out there.  Here is one:



QGIS is usually very quick when processing the big data sets.


Good luck!



Edited by Benson Shaw
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