File formats in detail — ModelCraft help

ModelCraft's model is in meters with Z (blue) up. Every format below is converted to or from that.

ModelCraft (.modelcraft)

What	Details
Open	Open (`⌘OCtrl+O`) or drop on the view. Files ending in `.json` are accepted too
Save	Save (`⌘SCtrl+S`), as a download
Keeps	Everything: geometry, faces and their colors, soft edges, groups, components, names, guides, scenes, the units, and the last camera and style
Leaves out	The undo history
Limit	200 MB

A file saved by a newer ModelCraft than yours is refused: "This model was saved by a newer ModelCraft (file version …). Update ModelCraft to open it." A file that is not a ModelCraft model says "This file is not a ModelCraft model (it is not JSON)." or "This is not a ModelCraft file we can open: …".

Collada (.dae)

Import and export. The best format for trading models with other 3D modelers.

Export: Collada 1.4.1, Z up, meters. One geometry per group or component definition; components are written once and placed by reference, so they stay shared. Faces with holes or concave outlines are split into triangles. Colors become materials. Loose edges are written as lines. Names that are not valid in the format are adjusted, and the exact name is kept alongside it.
Import: triangles, polygons (with holes), triangle fans and strips become faces; lines become edges. Node transforms, the file's up axis and its unit are applied. A node placed in several places, or a geometry used by several nodes, comes in as a component; other nodes come in as groups. Material colors (diffuse) become face colors.
Not imported: textures, skins and morphs, cameras, lights, some transform types (look-at and skew), and references to other files. The status bar counts them.
Lost on export: which edges are soft. On import, triangulated surfaces stay triangles, with the diagonals softened so flat areas still read as one surface.

OBJ (.obj)

Import and export.

Export: meters, Y up (the way OBJ readers expect), world coordinates. One object per group placement; components are written out in full at every placement. Faces with holes are split into triangles. Loose edges are written as lines. No materials file (.mtl), so no colors.
Import: read as meters with Y up. OBJ has no unit, so a model made in millimeters or inches arrives at the wrong size: scale it after import (see Rotate and scale). Materials are not read.
Limit: 2 million vertices or faces.

glTF (.glb, .gltf)

Export (.glb only): glTF 2.0 binary, meters, Y up. One mesh per definition, so components stay shared. Colors become materials. Loose edges are left out.
Import: .glb, or .gltf with its data inside the file. A .gltf that keeps its data in a separate .bin file is refused: "This glTF file keeps its data in a separate file (…). Export it as a single .glb and open that." Base colors become face colors; textures and extensions are not read.
Limit: 2 million vertices.

STL (.stl)

Export only, for 3D printing. Binary STL, millimeters (printer software reads STL as millimeters), Z up. Triangles only: groups, colors and loose edges are left out. Export closed solids for a clean print.

IFC (.ifc)

Export only, for BimCraft and other BIM programs. IFC4 with a project, a site, a building and one storey. Each top-level group or component becomes one building element proxy with its name; closed ones are written as solid shapes (faceted breps), open ones as surface models; holes in faces are kept. Loose geometry at the top level becomes one element called "Loose geometry". No types, properties, materials or storeys beyond one.

DWG (.dwg) and DXF (.dxf)

Import only, as lines on the ground. See Model on a site plan.

Read: lines, polylines (with arcs), 3D polylines, circles, arcs, and block references including arrays, from model space. Invisible objects (such as the hidden states of a dynamic block) are left out. Curves become 48 straight pieces per full turn.
Not read: splines, ellipses, hatches, text, dimensions, attributes, and anything in paper space.
Units: taken from the drawing when it says. If not, ModelCraft asks.
DXF must be ASCII. Binary DXF is refused.
DWG files from AutoCAD R13 up to the current format (AutoCAD 2018 and later; AC1012 to AC1032) are read by ModelCraft's own DWG reader, in the page; it is part of ModelCraft, so it works offline whenever ModelCraft does. Older versions (R12 and before) and badly damaged files cannot be read; save them as DXF.
Limits: coordinates more than 10,000 km from the origin, or more than 2 million line pieces, are refused.
Saving DWG or DXF is not built.

Not supported

ModelCraft cannot open or save SketchUp (.skp), 3DS, FBX, Rhino, STEP or IFC files. To bring in a model from SketchUp, export it from there as Collada (.dae) if your version can, or as OBJ.