If a polygon looks like it is invisible in Element, but appears normal in a regular 3d application, this is due to a Backwards/Reversed polygon Normal.
If you have a full 3d program (c4d, 3ds Max, etc) you can import the object into it, select the polygons that are facing backwards and reverse the normals. For example in Cinema 4D, if you select all of the polygons, the polygons that are blue are polygons that are facing backwards. If you select the display mode “Lines”, there are also pointers that show which way a polygon normal is facing. They should be pointing outwards.
In C4D you can select the blue polygons and go to Functions at the
top and select Reverse Normals, and that will fix the issue. Although
this a specific function in c4d, terminology is similar across different
Reversed normals can really only be fixed 100% in a full 3d program, however there is one solution that may help in Element alone. If you go the bottom of the material settings, there is an option called Draw Backfaces
. Enabling that will generate geometry on the back side of the polygon that has a reversed normal. This will not always fix all issues relating to reversed normals, as reflections and lighting may show up as reversed even though the geometry is visible, so fixing in a full 3d app is recommended for best results.
MODEL IS BLACK OR GREY ON IMPORT AND WON'T ACCEPT TEXTURES
This is due to the model not being exported with normals. Most programs have a checkbox in the obj export options whether to export with Normals or not. However some few programs do not have this option, for example Cinema 4D does not, in which case you can just import the C4D project file in Element.
If the model is not smooth, this is due to it not being exported with smoothing groups. Checking Auto Normals and adjusting the Edge Threshold value can help with this.
Normals are a piece of data an obj can be exported with, telling the program how to react to lighting properly.
Element 3D Auto Normals
If you do not have access to a 3D program in which you can
re-export with Normals, you can check Auto Normals and
adjust the smoothing with the Edge Threshold.
If your models are taking a while to import, the most obvious thing to look at would be the polygon count. For example if there are 1 million+ polygon faces on a model, it will take some time to import as that is a lot of info to load onto the GPU. If you can, optimize your models to be lower in polygon count and that will help it load faster.
If models are black or a solid color when adding textures, this is due to the model not being exported with Texture/UVW Coordinates out the full 3d application. If the model needs a specific wrap be sure to check your export settings program the model exported from, most programs will have an option to include Texutre/UVW Coordinates in the export. If the model doesn't need a specific texture wrap you can use Element UV Mapping settings
Element will convert all quad polygons to triangles as that is what the GPU needs to render. So having your model pre-triangulated before importing into Element can help speed up import so it doesn't have to do the triangle coversion process. Some programs will have an export option to export triangles in the obj settings.
Texture Import Speed
Textures that are multiples of 512x512 and of the power of two, will load faster. For example: 1024x1024, 2048x2048, 4096x4096, 8192x8192 or 512x1024, 1024x2048, 2048x4096, and 4096x8192. Also making sure that your texture has a dpi of 72 can help if the texture is looking blurry, on some mac machines larger relosutions can overload and blowout the quality. You can change this in Photoshop under Image/Image Size/Resolution, then resave the image.