STL vs STP file size

[pridbor]

I have just created STL and STP files for the exact same very small part. The former comes out as 3MB, and the latter 100k (rounded)

Does anybody know and can tell me that the extremely small file size for STP will render as detailed part as the much larger STL file?

And also, why/when would I want to use the STL format?

Thanks

Preben

Note: If I use the recommended setting for the STL file generation shown in a previous post, 2 %, then it almost doubles in size, 15MB.

 

[W01FM4N]

Hey Preben,

An STL file is a point cloud representing the vertices for the triangles and data that defines the normals (inside/outside), and depending on the deviation of the edges of the triangles relative to the true contour, the STL file can grow to a very large size. STL files are typically used for 3D printing on powder bed (metallic and non-metallic), resin, and filament machines. STL files can be generated by structured light scanning and utilized for contour/dimensional inspection/comparison.

STEP files primary purpose is to provide a standard method for exchanging 3D (solids) and 2D (surfaces) data between otherwise incompatible modeling software, etc.

Both STL and STEP files are usually ASCII text files, and can be compressed quite a bit.

There are software packages that can edit/modify mesh files, such as Rhinoceros. STEP files really aren't editable since the format doesn't have a "feature tree", making them basically DUMB SOLIDS.

So, STL and STEP files exist for different reasons, although if you're trying to recreate a design, a solid created from an STL file gives one a great head start.

Open those STL and STEP files with a text editor, and you can get a feel for the different file structures.

Sometimes STL files can created as binary data files, so the text will look like a bunch of garbage, but that same file will be smaller.

Been workng with CATIA and CREO/Pro Engineer for years, and STEP files are the easiest way to share 3D data. Finally, most Fluid, Stress, Thermal, etc. Analysis programs utilize STEP files.

Hope this sheads some valuable light on the subject.

Kurt

 

[Latitude]

This may not be the best analogy but maybe it helps.

This of a vector SVG file of this circle



Which is about 601 bytes because it essentially just says "make a circle"


But if I save it as an image it now colour pixel information for each pixel/point in space and so that takes up more space. Even a 100px x 71px image is about 2.89kb.


STL, to my understanding, is essentially a massive list of triangles and their positions and sizes where all of them put together approximate the shape you need. STEP can do more nuanced stuff like "make a circle of radius 0.5 centered at 0,0,0"

Again I am sure I've lost some nuance here but just in case it helps.

 

[dwc]

That doesn't surprise me at all.
When I look through some of my parts steps and stls I see that in general the stls are at least 2x, but sometimes 10x the step file sizes.
But there are cases where the stl is smaller.
That comes with the land, stls document the surface using lots of triangles, not terribly optimised for cylinders, for example, in general step uses volumes, a cylinder is a diameter and a length.

 

[Mika]

I just recently noticed that *.stl export "straighten" some surfaces if I have really big radius in part. *.step export works more better and for example PrusaSlicer can import *.step files.

 

[NateLiquidGravity]

The account of tessellation is determined by the STL export settings. https://help.alibre.com/articles/alibre-help-v27/stl-export-settings