# Land S/C and Merge Issues

**URL:** <https://forum.spis.org/t/land-s-c-and-merge-issues/1461>\
**Category:** SPIS\
**Created:** [11 February 2025 20:37 UTC](https://forum.spis.org/t/land-s-c-and-merge-issues/1461 "2025-02-11T20:37:38Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![amsi4509](https://forum.spis.org/letter_avatar_proxy/v4/letter/a/f0a364/32.png) [@amsi4509](https://forum.spis.org/u/amsi4509)\
**Post date:** [11 February 2025 20:37 UTC](https://forum.spis.org/t/land-s-c-and-merge-issues/1461/1 "2025-02-11T20:37:38Z")

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I have a spacecraft CAD model and a tessellated ground geometry file that I have successfully loaded into SPIS. Land S/C appears to work, as the spacecraft CAD translates appropriately. However, when I try to Merge the lander geometry and ground surface geometry, there are no Gmsh physical id of lander faces to merge available for me to select.

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**Author:** ![frejon](https://forum.spis.org/letter_avatar_proxy/v4/letter/f/7feea3/32.png) [@frejon](https://forum.spis.org/u/frejon)\
**Post date:** [17 February 2025 17:43 UTC](https://forum.spis.org/t/land-s-c-and-merge-issues/1461/2 "2025-02-17T17:43:37Z")

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Not sure what you mean, but maybe do all the merging in GMSH separately, and load the meshed (and optimised) mesh into SPIS

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**Author:** ![agozutok](https://forum.spis.org/letter_avatar_proxy/v4/letter/a/67e7ee/32.png) [@agozutok](https://forum.spis.org/u/agozutok)\
**Post date:** [4 March 2025 05:50 UTC](https://forum.spis.org/t/land-s-c-and-merge-issues/1461/3 "2025-03-04T05:50:39Z")

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Hello, I think you created the surface/lander geometry on SPIS however, did not define their physical properties before importing the .geo files to SPIS. You should check for the lander and ground surface geometry as well by selecting physical groups under geometry section on the left in UI.

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**Author:** ![amsi4509](https://forum.spis.org/letter_avatar_proxy/v4/letter/a/f0a364/32.png) [@amsi4509](https://forum.spis.org/u/amsi4509)\
**Post date:** [4 March 2025 14:31 UTC](https://forum.spis.org/t/land-s-c-and-merge-issues/1461/4 "2025-03-04T14:31:29Z")

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How would I go about defining the surface/lander physical properties prior to importing the .geo files? I can see my loaded files for the surface geometry and the lander geometry in the geometry section for the left, but are there more details about these files that I should be able to see?

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**Author:** ![ruard](https://forum.spis.org/letter_avatar_proxy/v4/letter/r/54ee81/32.png) [@ruard](https://forum.spis.org/u/ruard)\
**Post date:** [4 March 2025 15:04 UTC](https://forum.spis.org/t/land-s-c-and-merge-issues/1461/5 "2025-03-04T15:04:45Z")

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Edit your lander geometry .geo file with Gmsh to set the surface physical for the surfaces you want to merge with the ground geometry. Do not forget to set surface physicals for other surfaces of the lander geometry as well.

You have more details on how to use geometry features in SPIS Dust documentation which is packaged with SPIS 5.2.4: Spis-5.2.4/documentation/SPIS-Dust/TR 1-21505-v2\_SPIS-DUST-DDD\_2.2.pdf

You have also access to this documentation on the following webpage:  
[https://www.spis.org/software/spis/documentation/](https://www.spis.org/software/spis/documentation/)

Remark: Note that all dust module components are included in the latest releases  
(beta version 6.2.4 or last official release 6.1.0), so it should work just as well, if not better, than version 5.2.4.