geometry problem

[doriang]

Hi everyone.
I received an obj from a friend but this has a problem:
all the faces seem to be separate, so when I insert a subdivision surface I have a problem (as you can see in the attached images).
Does anyone know a solution for this?

[MarkoDer]

Go in edge mode and use the dissolve tool in order to create all quadrangle, the triangles must be avoided, after that use the optimize tool

[doriang]

Thank you so much. I had also arrived at this solution, trying everything.
Thanks again.

[doriang]

but instead of "dissolve" I use "melt" seems to work better .. I do not know why