# isosurface - hangs or crashes

**URL:** <https://discourse.slicer.org/t/isosurface-hangs-or-crashes/5560>\
**Category:** Support\
**Tags:** segmentation\
**Created:** [January 29, 2019, 2:34pm UTC](https://discourse.slicer.org/t/isosurface-hangs-or-crashes/5560 "2019-01-29T14:34:10Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![njeffery](https://avatars.discourse-cdn.com/v4/letter/n/8797f3/32.png) [@njeffery](https://discourse.slicer.org/u/njeffery)\
**Post date:** [January 29, 2019, 2:34pm UTC](https://discourse.slicer.org/t/isosurface-hangs-or-crashes/5560/1 "2019-01-29T14:34:10Z")

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Hi All,  
I am looking to create an isosurface to help with the selection of fiducials. However, when I try to create a surface (segment editor\>show 3D or grayscale model maker [no smoothing, and permutations of 0 to 0.5 decimation]) slicer just hangs (I left it for 67minutes in one instance) or crashes. The CT dataset is large (3GB), but I can load and create isosurfaces in Seg3D in about 90 secs (markup function in seg3d is pretty poor).

Using the latest version 4.10.1

Any suggestions?

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**Author:** ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)\
**Post date:** [January 30, 2019, 1:28am UTC](https://discourse.slicer.org/t/isosurface-hangs-or-crashes/5560/2 "2019-01-30T01:28:08Z")

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Everything indicates that you run out of memory. You can do one or more of these:

- crop (to the region of interest) and resample (to make the number of voxels about 300 along each axis) the volume before you do anything
- increase the virtual memory size (computation time will still remain long)
- smooth the segmentation (using Smoothing effect) before you click “Show 3D”
- disable model smoothing (drop-down menu of Show 3D) - it may make generation faster by a factor of 10-50x.

But maybe the simplest is to just use volume rendering for surface extraction. Choose a preset and use the offset slider to choose isosurface value. You may need to crop&resample input volume to fit into GPU memory.

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**Author:** ![njeffery](https://avatars.discourse-cdn.com/v4/letter/n/8797f3/32.png) [@njeffery](https://discourse.slicer.org/u/njeffery)\
**Post date:** [January 30, 2019, 8:28am UTC](https://discourse.slicer.org/t/isosurface-hangs-or-crashes/5560/3 "2019-01-30T08:28:42Z")

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many thanks Andras,  
I would be surprised if it were a memory problem - I have 96GB ram (I use the same machine for computational modelling). Unless there is some setup in slicer I have missed which means it is not using the memory correctly? I will check out the volume rendering options, though I have struggled with the landmarking of surfaces with volume rendering in the past - landmarks tend to sink through the surface.  
best and thanks