Sketchup Models

kenmo

Any tips on how to clean up Sketchup models for use in DAZ3D? I am thinking mostly about car models as there seems to be more car models available for Sketchup then any other file version. And why more Sketchup car models than DAZ has available.

I've tried the SKP importer for Blender. And it works fine. But the topology is terrible. And would require a lot of manual work.

I'm using Sketchup Make (free version) and the only export option is DAE which is ugly when imported into DAZ or 3D Coat or anything else.

Not sure why Sketchup models are such a mess.

Cheers

FSMCDesigns

Sketchup models are pretty inefficient and will usually need work, it's due to how the modeler works and the workflow. Users with previous modeling skills will do better creating in sketchup, but in general you will need to do modifications for best results in other apps like DS.

Mattymanx

I have looked at SKP files in the past in hopes of converting some, but outside of the apps they are meant for, SKP files will be a royal mess.  I am guessing it has to do with how Sketchup modeling works compared to regular box modeling or sculpting.

McGyver

kenmo said:

Any tips on how to clean up Sketchup models for use in DAZ3D? I am thinking mostly about car models as there seems to be more car models available for Sketchup then any other file version. And why more Sketchup car models than DAZ has available.

I've tried the SKP importer for Blender. And it works fine. But the topology is terrible. And would require a lot of manual work.

I'm using Sketchup Make (free version) and the only export option is DAE which is ugly when imported into DAZ or 3D Coat or anything else.

Not sure why Sketchup models are such a mess.

Cheers

Its not SketchUp, it's the individual who makes the models... SketchUp allows you to model "too easily" and this invites lazy modelers to invert normals, model using only N-gons (as opposed to quads or tris), leave behind duplicate vertices, make terrible UV mapping mistakes and other cardinal sins of modeling.

Also most people are only aware of the "base" toolset that comes with the free version of SketchUp, and are completely unaware of the dozens of free plugins that are available, that transform SketchUp into a fairly competent modeling application.

I generally model correctly and only have to deal with crappy modeling if I'm working on a project with someone, which usually causes me to have to redo all their garbage, so I do know a lot about fixing crappy modeling... and honestly, some great looking models have been terribly made.

If you are using the current free version of Sketchup (the online only version), ditch it and get the last version which could still use plugins (Make 2017).

As far a tips... that's really hard to nail down, as there are tons of things to be aware of...

I'll start with two tips...

Tip One...

A big tip I could offer is to view the model in monochrome view before trying export it... (you'll understand why in a moment)

To access that, go to View > Face Style > Monochrome... Unless the person who made the model changed the default colors, all the front faces (outward facing normals) should be white and back faces (the reverse side, inward facing normals) should be blue-grey.

A well made model should be entirely white... but most likely what you'll see is a patchwork of white and gray... that's bad... worse yet, sometimes people actually apply a texture to the reverse face instead of the front face making repairs harder... before even bothering to fix anything, you should make note of a couple of reversed faces (if there are any) and go back to "Shaded With Textures"... (View > Face Style > Shaded With Textures).

If there are more than a couple of textured faces that are reverse, it might not be worth fixing because at some point the amount of time involved will exceed the value... but if you still want to try, basically you are going to have select the whole model (assuming it's not comprised of multiple groups and components)...(more on that later)... and (in SU2017) go to Window > Default Tray > Materials. 
The default tray window should open, go down to Materials and on right side under the " X" button (close button) there should be three icons... the top looks like two stacked squares with a triangle and a plus sign in them... in the middle, a cube with circle with a plus sign in it on one corner... and on the bottom a square split diagonally into two colors (representing the default colors)...(hopefully white and grey)...
Select the Paint Bucket tool and click on that two color icon to select the default color. 
Apply that to the whole model... if it's made of lots of components and groups that might be a problem and you may have to "Explode" the whole model... that basically means ungrounding all the groups and components... blegh.

Now about reversing those flipped faces... also blegh...

There is a plugin to automate this, but it's old and works spottily... but it might take some tedium out of the process...

https://sketchucation.com/pluginstore?pln=Vbfr

There is also this one, but I've never used it... it might be more efficient, the author (TIG) is a real expert plugin writer.

https://sketchucation.com/pluginstore?pln=FixReversedFaceMaterials

Otherwise, you are going to have to manually flip each reversed face...

Select the face, click the right mouse button and chose "Reverse Face".

If you are really lucky, you'll find a model that requires little work.

 

Tip 2...

Deleting unused geometry...

A big huge issue with a lot of models is people think that by erasing something, it's actually deleted... this is especially problematic with exploded groups and erased components.

To get rid of this invisible garbage go to > Model Info... in the menu box that opens on the left side is a list... Animation, Components, Credits, etc...

Chose "Statistics" 

In the new window that opens inside, go down to the bottom left and click the "Purge Unused" button.

Congratulations, you just flushed all the unused garbage out of the model... this my have little impact, or it may significantly lighten the model... either way, it makes it easier to export...

ALWAYS DO THIS AS THE LAST STEP BEFORE EXPORTING!

I'll throw in a third tip, but I don't have much time to explain in detail...

On like 90% of the models it is going to make more sense to explode the model before exporting... the exporter or importer is going to have to sift through a ton of unnecessary group and component garbage as it converts it... in most cases you can't use those groups the way they were intended, so it just bogs down the model and leads to little errors.

Sorry but I don't have time to explain the process in detail, but could later if you are interested.

 

I'll make another suggestion... 

If you like to use SketchUp models, may I suggest getting Ultimate Unwrap3D Pro it's $60, and even if you don't use it for the UV mapping its intended for, it has one of the best SketchUp importer I've ever used... it preserves textures and will export to OBJ without involving Blender (but the model scale get messed up so you may still need to mess around with it in Blender if you prefer that to DS for tweaking)

https://www.unwrap3d.com/u3d/index.aspx

Sorry I'm cutting this short, but I'm running out of time, and to be honest 95% of the times I've responded to posts like this, the OP was not really looking actual tips or suggestions but merely asking "Where's the Fix Everything Button?" They ask and never respond again and I don't know if it was helpful or they were just like "Eff this, too much to read, don't care"...

If you really are interested I can share more info, including screen shots if necessary and I'm very happy to help... so just let me know.

Have a great day and I hope this was helpful.

kenmo

Thanks for the tips. I've used the trial version of unwarp3d before. But for uv maping and went with UV Mapper instead. Now I use 3DCoat for UV mapping. But it is certainly worth to look at Unwrap3d if it can cure some of the nasty topology in Sketchup models. 

McGyver

kenmo said:

Thanks for the tips. I've used the trial version of unwarp3d before. But for uv maping and went with UV Mapper instead. Now I use 3DCoat for UV mapping. But it is certainly worth to look at Unwrap3d if it can cure some of the nasty topology in Sketchup models. 
 

Ultimate Unwrap3D won't fix the topography, you have to fix modeling related problems yourself.

UU3D is just a more reliable way of getting a model over to DS... 

I make a lot of stuff in SketchUp and after I make a model I can just import the SKP directly into UU3D.

One issue SketchUp has always had is meshes tend to "break" when exported (parts of the mesh randomly become "unwelded")... with UU3D I find it easier to "weld" the mesh back than in Blender or most other programs, generally I just import the SKP by opening it in UU3D, when the import dialogue box appears, I make sure to check "weld vertices", once it opens you'll see the model automatically had all faces triangulated... if the model was thoughtful made, you can select the whole model and "untriangulate" it to save some polygons... if it's not a very well constructed model it probably won't change more than a handful of faces.

But I stress that this is not any sort of retopology, it's just eliminating unnecessary edges.

If the model is satisfactory you can then export it in OBJ format to DS.

FSMCDesigns

McGyver said:

kenmo said:

Thanks for the tips. I've used the trial version of unwarp3d before. But for uv maping and went with UV Mapper instead. Now I use 3DCoat for UV mapping. But it is certainly worth to look at Unwrap3d if it can cure some of the nasty topology in Sketchup models. 
 

Ultimate Unwrap3D won't fix the topography, you have to fix modeling related problems yourself.

UU3D is just a more reliable way of getting a model over to DS... 

I make a lot of stuff in SketchUp and after I make a model I can just import the SKP directly into UU3D.

One issue SketchUp has always had is meshes tend to "break" when exported (parts of the mesh randomly become "unwelded")... with UU3D I find it easier to "weld" the mesh back than in Blender or most other programs, generally I just import the SKP by opening it in UU3D, when the import dialogue box appears, I make sure to check "weld vertices", once it opens you'll see the model automatically had all faces triangulated... if the model was thoughtful made, you can select the whole model and "untriangulate" it to save some polygons... if it's not a very well constructed model it probably won't change more than a handful of faces.

But I stress that this is not any sort of retopology, it's just eliminating unnecessary edges.

If the model is satisfactory you can then export it in OBJ format to DS.

This is pretty much my experence also with sketchup models and using UUW3D. It also makes it easier to redo UVMaps since many sketchup models are not UVMapped

kenmo

When Vue had their Cornucopia3D store they sold a Sketchup plug that exported the Sketchup model as a Vue vob model. I played with the trial version and it worked excellent. I only wished I had purchased before they closed their store.

McGyver

Another alternative way of getting models out of SketchUp is to export it as a DAE (remember to check "triangulate" in the export options dialogue box before exporting), and then open it in Blender... You'll still have to weld the vertices in Blender... I forget what that process is, and I'm not on my computer now (iPad), after that, export it from Blender as an OBJ. 

But you'll still have to fix it SketchUp before you do that... because lazy modeling won't fix itself.

Also, you don't necessarily always need to re-weld the mesh, if it's just something simple like a chair or a crate, the broken mesh isn't really a big deal... if it's like car, then yeah, it starts to matter.

Since I don't know how much you know about modeling and meshes, it occurred to me that I keep saying stuff about "welding vertices" and I don't think I explained that... The model aka "the mesh" is made of polygons... a proper mesh (lets say a sphere) is made of interconnected polygons... each polygon is attached to the one adjacent and together they form a continuous surface... if for some reason sections of polygons are selected as separate zones, they are no longer part of the mesh... it's like they are still in the exact same position, but they are separate... this can screw up reflections, cause light leakage or weirdly stretch textures and assorted junk like that... sometimes meshes break accidentally and welding is just sticking everything back where it belongs.

I really should write a tutorial one day on how to fix and use SU models in DAZ and Poser... nobody will read it, but it'll keep me busy.

Artini

Yes, there are a lot, lot (many, many) free 3D Models there, but it is a pain to export them to anything else.

They changing their file format so often, as well.

Does anybody has SketchUp Pro and has tried to export 3D models from it?

 

McGyver

Artini said:

Yes, there are a lot, lot (many, many) free 3D Models there, but it is a pain to export them to anything else.

They changing their file format so often, as well.

Does anybody has SketchUp Pro and has tried to export 3D models from it?

I have SketchUp 8 Pro on an older computer, the OBJ export still had broken mesh issues... the last version of Pro I tried was probably 2017... it seemed to export smaller models okay, but when I tried a much larger model I found parts of the mesh had become unwelded.

Part of the reason I never upgraded Pro past 8 was it never really seemed like Google bothered to fix the broken mesh thing and that was the dealbreaker to me... then they sold SketchUp to Trimble and Trimble turned it into a subscription after SU 2017... and since my very existence is in conflict with paying for subscription software, Pro ain't never gonna happen for me again.

hacsart

There is a free app called Poseray used to convert 3D model meshes into POV-Ray scenes (POV-Ray command line was my first render engine!) however it can be if use for .skp files.

Export the Sketchup model as a .3ds mesh  (sometimes in parts for opening doors, hoods, tires etc.). Import each 3ds file up in Poseray. like most Sketchup models. it will be blocky with edges not rounded well. Check the "groups" tab at the top in Poseray. TSelect  "weld vertices" and once it completes, select and check "recalculate normals". It will run for a few seconds and on completion..the model is smoothed. Huge difference. Export as .obj and import into Daz and apply textures. It's not always perfect, but it is a time saver.

 

FSMCDesigns

ultimate unwrap 3D has a plugin for the sketchup format and imports them fairly well and exports to lots of formats

McGyver

Free OBJ exporters that I've used:

TIG's OBJ Exporter v.3.0- https://sketchucation.com/pluginstore?pln=OBJexporter

thomthom's Quadface Tools v.0.14.1- https://sketchucation.com/pluginstore?pln=QuadFaceTools  (Comes with an Obj exporter built in)

Whaat's SketchUV v.1.0- http://www.smustard.com/script/SketchUV   or  https://extensions.sketchup.com/extension/5ed6aba8-16fa-4071-81f5-7938cb94fd3e/sketch-uv  The last one might be a newer version (1.0.2)... Both versions come with an OBJ exporter.

These all do a decent job at exporting the model "as is"... but the issues with polygons becoming unwelded still exists in them... 

If the model has flipped faces or bad topography it's still up to the user to fix it as nothing really fixes that automatically.

Also remember to triangulate faces before exporting a model from SketchUp when using DAE or OBJ.

Note: the above plugins need to be installed into SketchUp to work.

To install a plugin in SketchUp.

1. In SketchUp, select Extensions > Extension Manager. The Extension Manager window appears.
2. Click the Install Extension button.
3. In the Open dialog box that appears, navigate to the .rbz file saved to your computer, select the file, and click OK (Microsoft Windows) or Open (Mac OS X).
4. When SketchUp warns you about installing only extensions from trusted sources, click Yes to proceed and install your extension. (This assumes you do, in fact, trust the source of your extension.)

kenmo

The biggest problem with DAE is they give me more problems and issues then SKP files. And YES when exporting from Sketchup I do select the triangulate when exporting.

kenmo

McGyver said:

Another alternative way of getting models out of SketchUp is to export it as a DAE (remember to check "triangulate" in the export options dialogue box before exporting), and then open it in Blender... You'll still have to weld the vertices in Blender... I forget what that process is, and I'm not on my computer now (iPad), after that, export it from Blender as an OBJ. 

But you'll still have to fix it SketchUp before you do that... because lazy modeling won't fix itself.

Also, you don't necessarily always need to re-weld the mesh, if it's just something simple like a chair or a crate, the broken mesh isn't really a big deal... if it's like car, then yeah, it starts to matter.

Since I don't know how much you know about modeling and meshes, it occurred to me that I keep saying stuff about "welding vertices" and I don't think I explained that... The model aka "the mesh" is made of polygons... a proper mesh (lets say a sphere) is made of interconnected polygons... each polygon is attached to the one adjacent and together they form a continuous surface... if for some reason sections of polygons are selected as separate zones, they are no longer part of the mesh... it's like they are still in the exact same position, but they are separate... this can screw up reflections, cause light leakage or weirdly stretch textures and assorted junk like that... sometimes meshes break accidentally and welding is just sticking everything back where it belongs.

I really should write a tutorial one day on how to fix and use SU models in DAZ and Poser... nobody will read it, but it'll keep me busy.

 I've been modeling for close to 20 years. First with Wings3D then Hexagon3d. I now model in Silo3D, Moi3D & 3D Coat. I am slowly learning Blender 2.8x but only for modeling and not too keen on add-ons like Boxcutter, Hardops, Fluent or Kitops. Too many issues with shading and normals when using those addons.

Some stuff I've modeled over the years...

 

 

 

 

 

 

 

kenmo

The above well ALL created by me from scratch. No kitbashing or parts or models downloaded from the web. ALL my creations.

kyoto kid

...you are light years ahead of me.  I tried pretty all of those. Hexagon was just too unstable and kept freezing up while Wings was hard to work with because of their choice of colours for their UI (grey text on a light grey background was just too much strain on the old eyes). I have Blender 2.8 and (finally a more "humane "UI) but it still is taking time and there are just some concepts about more involved modelling I have difficulty in grasping. Was much better at building physical items with my hands.

FirstBastion

kenmo said:

The above well ALL created by me from scratch. No kitbashing or parts or models downloaded from the web. ALL my creations.

 Very good job on the HotRod !

Bendinggrass

McGyver said:

kenmo said:

Any tips on how to clean up Sketchup models for use in DAZ3D? I am thinking mostly about car models as there seems to be more car models available for Sketchup then any other file version. And why more Sketchup car models than DAZ has available.

I've tried the SKP importer for Blender. And it works fine. But the topology is terrible. And would require a lot of manual work.

I'm using Sketchup Make (free version) and the only export option is DAE which is ugly when imported into DAZ or 3D Coat or anything else.

Not sure why Sketchup models are such a mess.

Cheers

Its not SketchUp, it's the individual who makes the models... SketchUp allows you to model "too easily" and this invites lazy modelers to invert normals, model using only N-gons (as opposed to quads or tris), leave behind duplicate vertices, make terrible UV mapping mistakes and other cardinal sins of modeling.

Also most people are only aware of the "base" toolset that comes with the free version of SketchUp, and are completely unaware of the dozens of free plugins that are available, that transform SketchUp into a fairly competent modeling application.

I generally model correctly and only have to deal with crappy modeling if I'm working on a project with someone, which usually causes me to have to redo all their garbage, so I do know a lot about fixing crappy modeling... and honestly, some great looking models have been terribly made.

If you are using the current free version of Sketchup (the online only version), ditch it and get the last version which could still use plugins (Make 2017).

As far a tips... that's really hard to nail down, as there are tons of things to be aware of...

I'll start with two tips...

Tip One...

A big tip I could offer is to view the model in monochrome view before trying export it... (you'll understand why in a moment)

To access that, go to View > Face Style > Monochrome... Unless the person who made the model changed the default colors, all the front faces (outward facing normals) should be white and back faces (the reverse side, inward facing normals) should be blue-grey.

A well made model should be entirely white... but most likely what you'll see is a patchwork of white and gray... that's bad... worse yet, sometimes people actually apply a texture to the reverse face instead of the front face making repairs harder... before even bothering to fix anything, you should make note of a couple of reversed faces (if there are any) and go back to "Shaded With Textures"... (View > Face Style > Shaded With Textures).

If there are more than a couple of textured faces that are reverse, it might not be worth fixing because at some point the amount of time involved will exceed the value... but if you still want to try, basically you are going to have select the whole model (assuming it's not comprised of multiple groups and components)...(more on that later)... and (in SU2017) go to Window > Default Tray > Materials. 
The default tray window should open, go down to Materials and on right side under the " X" button (close button) there should be three icons... the top looks like two stacked squares with a triangle and a plus sign in them... in the middle, a cube with circle with a plus sign in it on one corner... and on the bottom a square split diagonally into two colors (representing the default colors)...(hopefully white and grey)...
Select the Paint Bucket tool and click on that two color icon to select the default color. 
Apply that to the whole model... if it's made of lots of components and groups that might be a problem and you may have to "Explode" the whole model... that basically means ungrounding all the groups and components... blegh.

Now about reversing those flipped faces... also blegh...

There is a plugin to automate this, but it's old and works spottily... but it might take some tedium out of the process...

https://sketchucation.com/pluginstore?pln=Vbfr

There is also this one, but I've never used it... it might be more efficient, the author (TIG) is a real expert plugin writer.

https://sketchucation.com/pluginstore?pln=FixReversedFaceMaterials

Otherwise, you are going to have to manually flip each reversed face...

Select the face, click the right mouse button and chose "Reverse Face".

If you are really lucky, you'll find a model that requires little work.

 

Tip 2...

Deleting unused geometry...

A big huge issue with a lot of models is people think that by erasing something, it's actually deleted... this is especially problematic with exploded groups and erased components.

To get rid of this invisible garbage go to > Model Info... in the menu box that opens on the left side is a list... Animation, Components, Credits, etc...

Chose "Statistics" 

In the new window that opens inside, go down to the bottom left and click the "Purge Unused" button.

Congratulations, you just flushed all the unused garbage out of the model... this my have little impact, or it may significantly lighten the model... either way, it makes it easier to export...

ALWAYS DO THIS AS THE LAST STEP BEFORE EXPORTING!

I'll throw in a third tip, but I don't have much time to explain in detail...

On like 90% of the models it is going to make more sense to explode the model before exporting... the exporter or importer is going to have to sift through a ton of unnecessary group and component garbage as it converts it... in most cases you can't use those groups the way they were intended, so it just bogs down the model and leads to little errors.

Sorry but I don't have time to explain the process in detail, but could later if you are interested.

 

I'll make another suggestion... 

If you like to use SketchUp models, may I suggest getting Ultimate Unwrap3D Pro it's $60, and even if you don't use it for the UV mapping its intended for, it has one of the best SketchUp importer I've ever used... it preserves textures and will export to OBJ without involving Blender (but the model scale get messed up so you may still need to mess around with it in Blender if you prefer that to DS for tweaking)

https://www.unwrap3d.com/u3d/index.aspx

Sorry I'm cutting this short, but I'm running out of time, and to be honest 95% of the times I've responded to posts like this, the OP was not really looking actual tips or suggestions but merely asking "Where's the Fix Everything Button?" They ask and never respond again and I don't know if it was helpful or they were just like "Eff this, too much to read, don't care"...

If you really are interested I can share more info, including screen shots if necessary and I'm very happy to help... so just let me know.

Have a great day and I hope this was helpful.

McGyver, thanks so much. I had looked at Sketchup a number of times, but now I think I will give it a go at using. Your tips and info is fantastic, and I for one really appreciate it... plus your humour.

Keep safe and well.

Randy 

kenmo

Downloaded Ultimate Unwrap3D Pro and some of the features in the demo are disabled that I would need to test the app.

Also it seems way too complicated compared to UV Mapper Classic or even 3D Coats uv mapping features.

I really do not need another UV Mapping app when I have all I need in 3D Coat.

So, I will not be spending money on this overly complicated app.

Cheers

McGyver

Kenmo said:

I've been modeling for close to 20 years. First with Wings3D then Hexagon3d. I now model in Silo3D, Moi3D & 3D Coat. I am slowly learning Blender 2.8x but only for modeling and not too keen on add-ons like Boxcutter, Hardops, Fluent or Kitops. Too many issues with shading and normals when using those addons.

Some stuff I've modeled over the years...

.......

The above well ALL created by me from scratch. No kitbashing or parts or models downloaded from the web. ALL my creations.

.......

The biggest problem with DAE is they give me more problems and issues then SKP files. And YES when exporting from Sketchup I do select the triangulate when exporting.

Those are very good looking, well constructed models, especially the hot rod.

I wasn't trying to be a jerk or anything by over explaining and I'm sorry if I made it seem that way.

Most of the things in life that I've learned, were from someone else, be it from an actual person, or from a book or article. 

If I have information I think is useful to someone, I'm happy to share it and most of the times that I do respond to a question, I try to answer the question asked, but also include whatever little extra information that might extend beyond what it seems like they might need, not only for them, but because maybe a year or five later someone else might be Googling that same question and hopefully if they find that post, it will help them.

Lots of times that I've Googled a question I have found old threads with half answered questions, wrong answers, enigmatic answers or the person responding clearly didn't read the original questions (like for example someone asking how to do something using a free program and the response is "you could use this $5000 program to do it much easier"... dude, if they had 5k to spend they probably wouldn't be asking the question in a free software forum)... So in general, I probably over-answer, but it's not because I think I'm smart, it's because I know I'm not and I'm just sharing what I've found to be useful information and because most of the time I learned anything it was because the person who was explaining didn't just give a cursory answer, they actually explained it in a way that a person who'd be asking that question in the first place probably needed it explained.

So sorry if what I wrote was insulting or seemed demeaning, it wasn't meant to be.

 

Kenmo said:
Downloaded Ultimate Unwrap3D Pro and some of the features in the demo are disabled that I would need to test the app.

Also it seems way too complicated compared to UV Mapper Classic or even 3D Coats uv mapping features.

I really do not need another UV Mapping app when I have all I need in 3D Coat.

So, I will not be spending money on this overly complicated app. 

Cheers

Sorry, if I wasted your time, I never tried the demo, but I took a shot on it and it did what I needed it for, I too have 3D Coat and the UV mapping tools are quite different (especially the auto-mapping), but while those features are great, it doesn't convert SKPs... UV mapper Classic is essentially a dead program, and if I recall correctly, while it does have a weld feature there is virtually no support other than a bunch of assorted random old tutorials with dead links and missing images (things may have changed, I haven't checked on UVMC in a couple of years)...
Currently using the version of UU3D Pro that I have, the SKP import feature works very well... I'm sorry if your experience was not good, but I was only suggesting it for its export/import features and easy welding ability. 

McGyver

Bendinggrass said:

McGyver said:

kenmo said:

Any tips on how to clean up Sketchup models for use in DAZ3D? I am thinking mostly about car models as there seems to be more car models available for Sketchup then any other file version. And why more Sketchup car models than DAZ has available.

I've tried the SKP importer for Blender. And it works fine. But the topology is terrible. And would require a lot of manual work.

I'm using Sketchup Make (free version) and the only export option is DAE which is ugly when imported into DAZ or 3D Coat or anything else.

Not sure why Sketchup models are such a mess.

Cheers

Its not SketchUp, it's the individual who makes the models... SketchUp allows you to model "too easily" and this invites lazy modelers to invert normals, model using only N-gons (as opposed to quads or tris), leave behind duplicate vertices, make terrible UV mapping mistakes and other cardinal sins of modeling.

Also most people are only aware of the "base" toolset that comes with the free version of SketchUp, and are completely unaware of the dozens of free plugins that are available, that transform SketchUp into a fairly competent modeling application.

I generally model correctly and only have to deal with crappy modeling if I'm working on a project with someone, which usually causes me to have to redo all their garbage, so I do know a lot about fixing crappy modeling... and honestly, some great looking models have been terribly made.

If you are using the current free version of Sketchup (the online only version), ditch it and get the last version which could still use plugins (Make 2017).

As far a tips... that's really hard to nail down, as there are tons of things to be aware of...

I'll start with two tips...

Tip One...

A big tip I could offer is to view the model in monochrome view before trying export it... (you'll understand why in a moment)

To access that, go to View > Face Style > Monochrome... Unless the person who made the model changed the default colors, all the front faces (outward facing normals) should be white and back faces (the reverse side, inward facing normals) should be blue-grey.

A well made model should be entirely white... but most likely what you'll see is a patchwork of white and gray... that's bad... worse yet, sometimes people actually apply a texture to the reverse face instead of the front face making repairs harder... before even bothering to fix anything, you should make note of a couple of reversed faces (if there are any) and go back to "Shaded With Textures"... (View > Face Style > Shaded With Textures).

If there are more than a couple of textured faces that are reverse, it might not be worth fixing because at some point the amount of time involved will exceed the value... but if you still want to try, basically you are going to have select the whole model (assuming it's not comprised of multiple groups and components)...(more on that later)... and (in SU2017) go to Window > Default Tray > Materials. 
The default tray window should open, go down to Materials and on right side under the " X" button (close button) there should be three icons... the top looks like two stacked squares with a triangle and a plus sign in them... in the middle, a cube with circle with a plus sign in it on one corner... and on the bottom a square split diagonally into two colors (representing the default colors)...(hopefully white and grey)...
Select the Paint Bucket tool and click on that two color icon to select the default color. 
Apply that to the whole model... if it's made of lots of components and groups that might be a problem and you may have to "Explode" the whole model... that basically means ungrounding all the groups and components... blegh.

Now about reversing those flipped faces... also blegh...

There is a plugin to automate this, but it's old and works spottily... but it might take some tedium out of the process...

https://sketchucation.com/pluginstore?pln=Vbfr

There is also this one, but I've never used it... it might be more efficient, the author (TIG) is a real expert plugin writer.

https://sketchucation.com/pluginstore?pln=FixReversedFaceMaterials

Otherwise, you are going to have to manually flip each reversed face...

Select the face, click the right mouse button and chose "Reverse Face".

If you are really lucky, you'll find a model that requires little work.

 

Tip 2...

Deleting unused geometry...

A big huge issue with a lot of models is people think that by erasing something, it's actually deleted... this is especially problematic with exploded groups and erased components.

To get rid of this invisible garbage go to > Model Info... in the menu box that opens on the left side is a list... Animation, Components, Credits, etc...

Chose "Statistics" 

In the new window that opens inside, go down to the bottom left and click the "Purge Unused" button.

Congratulations, you just flushed all the unused garbage out of the model... this my have little impact, or it may significantly lighten the model... either way, it makes it easier to export...

ALWAYS DO THIS AS THE LAST STEP BEFORE EXPORTING!

I'll throw in a third tip, but I don't have much time to explain in detail...

On like 90% of the models it is going to make more sense to explode the model before exporting... the exporter or importer is going to have to sift through a ton of unnecessary group and component garbage as it converts it... in most cases you can't use those groups the way they were intended, so it just bogs down the model and leads to little errors.

Sorry but I don't have time to explain the process in detail, but could later if you are interested.

 

I'll make another suggestion... 

If you like to use SketchUp models, may I suggest getting Ultimate Unwrap3D Pro it's $60, and even if you don't use it for the UV mapping its intended for, it has one of the best SketchUp importer I've ever used... it preserves textures and will export to OBJ without involving Blender (but the model scale get messed up so you may still need to mess around with it in Blender if you prefer that to DS for tweaking)

https://www.unwrap3d.com/u3d/index.aspx

Sorry I'm cutting this short, but I'm running out of time, and to be honest 95% of the times I've responded to posts like this, the OP was not really looking actual tips or suggestions but merely asking "Where's the Fix Everything Button?" They ask and never respond again and I don't know if it was helpful or they were just like "Eff this, too much to read, don't care"...

If you really are interested I can share more info, including screen shots if necessary and I'm very happy to help... so just let me know.

Have a great day and I hope this was helpful.

McGyver, thanks so much. I had looked at Sketchup a number of times, but now I think I will give it a go at using. Your tips and info is fantastic, and I for one really appreciate it... plus your humour.

Keep safe and well.

Randy 

Thank you, I'm glad you found some of this useful.  
Please note my later post about free plugin alternatives to Ultimate Unwrap3D Pro...
I wasn't aware it's demo doesn't allow you to test the export/import features, so I'm adding this disclaimer that if you do end up purchasing it, be aware that the UV mapping feature might not be as simple or easy to use as UV Mapper Classic, Roadkill or other UV mapping tools out there... If you do purchase it, do so only because you want access to the import/export features and the weld feature, the mapping tool is  "Ok", but nothing special.

UU3D does not have a lot of tutorials, so if you want to use its mapping features, you might end up having to figure stuff out on your own... which is frustrating since it doesn't have a forum where one can ask questions.

I purchased UU3D Pro because I still make some models in SketchUp and it's very convenient for me to use that workflow to convert them to other formats, especially if I want to use them in DS or Poser... I want to stress that spending $60 for UU3D, just for the exporters/importers might not be a fulfilling purchase for everyone, or seem an unnecessary frivolous expense.

Anyway... I'm probably prattling on... have a great day and good luck.

FSMCDesigns

A fellow forum user pointed me to this free software that can import and export sketchup models https://pcon-planner.com/en/ ; looks like it has some other cool options also

McGyver

FSMCDesigns said:

A fellow forum user pointed me to this free software that can import and export sketchup models https://pcon-planner.com/en/ ; looks like it has some other cool options also

Thats pretty interesting, I've never heard of this one before. I'll keep that in mind.

run4real

I work since 2 years with pCon Planner and use it together with Sketchup 8 to 2017 and can confirm it works like a charm!

FSMCDesigns

modeller said:

I work since 2 years with pCon Planner and use it together with Sketchup 8 to 2017 and can confirm it works like a charm!

Cool, before I install it, how does it render?

run4real

FSMCDesigns said:

modeller said:

I work since 2 years with pCon Planner and use it together with Sketchup 8 to 2017 and can confirm it works like a charm!

Cool, before I install it, how does it render?

Attached is an imported lightspot from Sketchup as an example

 

FSMCDesigns

Nice, thanks for that

run4real

FSMCDesigns said:

Nice, thanks for that

 

2 more very quick renders directly imported from Sketchup or Warehouse as skp file (nothing special) in order that you get a feeling for the render engine, it's not comparable with iray and only for illustration purposes

FSMCDesigns

Thanks, the promos I saw in a video looked pretty comparable to Iray which is why I asked. Is it possible to export any of the rooms you create with it to OBJ?