I am using getGeomExtents() to get bounding box. But the bounding box I am getting from getGeomExtents() is very large which also includes invisible objects.

getGeomExtents() ignores visibility of entities and layers. It includes invisible entities in extents. To get extents of visible geometry see the following threads in our forum:

https://forum.opendesign.com/showthread.php?18480-Problem-computing-extents-for-model-space&highlight=abstractViewPE

https://forum.opendesign.com/showthread.php?16342-View-Extents-problem