creating support for a surface I created an stl file of bathymetry using Matlab and the results can be seen in the two pictures below in Blender. The problem I have is that it is very thin with overhangs. I would like to add some kind of support. For example put a solid block underneath it like in the third picture.







I can't seem to figure out how to do this in Blender and if I try to fix the stl file in Blender it puts a surface through my original surface. I also tried to use Microsoft 3D printing repair but it takes hours to queue.
How to I change my stl file so it has enough support to be printed?
You generated a simple surface. You do however need a closed body to print. You might get away with using that surface as a cutter for a block and removing the top half, but there is an easier way using blender:


Select the whole ara with A
Extrude with E then Z to constrain direction
pull until you have an item that is fully thick everywhere
Scale the currently selected, extruded vertices with S then Z then 0 to force them all into the same plane
possibly move the vertices down till they all are below the bottom surface


Now you have a positive thickness, solid body! Run a simple "remove double vertices" on this bottom if you want to reduce file size, but there you go! Export as STL and print!