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If you want to map an equirectangular image texture to a sphere - like a map of the earth to a sphere - is there any necessity to use an UV map ? Or can I simply use the generated texture coordinates ? In general, when do you choose for UV unwrapping and when to use generated texture coordinates ?

I don't think this question is a duplicate with this question because these answers all start with the uv unwrapping method and I want to know if UV unwrapping or generated texture coordinates works best for my specific question. And I also would like to learn some general guidelines when choosing uv unwrapped vs generated texture coordinates

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  • related: http://blender.stackexchange.com/questions/3315/how-to-get-perfect-uv-sphere-mercator-projection – p2or Jan 19 '16 at 13:00
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    I still don't agree that this question is a duplicate. I don't ask what is the best way to unwrap a sphere but I ask what is the best way to map an image texture to a sphere ... Please explain why my question is a duplicate –  Jan 19 '16 at 23:37
  • I agree that this is most certainly not a dupe. This question merely uses a sphere as an incidental example and is not asking about the best way to unwrap a sphere; rather about pros and cons and use cases of generated vs. UV coords. – PGmath Jan 20 '16 at 02:41
  • @JanScherders Since you've asked how texturing a sphere, it's a dupe (IMO). When you really think about it there must be a reason why the answers starting with uv unwrapping, BTW: answers have nothing to do with questions. If the answers of the found questions doesn't solve your issue why not simply write: "Based on this question i'd like to know..." instead of "This is not a dupe" - this is less offensive and better practice (IMO). Also duplicates are not bad, they are helping future visitos to find the correct answer. Anyway, don't take it personal. – p2or Jan 20 '16 at 10:12
  • @poor Thanks for your feedback. I still have to get used to the idea that duplicates are not bad. Everytime when someone tells me I added a duplicate I feel like I have done something wrong. And I will certainly try to improve my language. Thanks, poor !! –  Jan 20 '16 at 12:59
  • @JanScherders Though I still didn't agree that this was a dupe, poor is right that dupes aren't bad at all, especially considering that SE's search functionality leaves a lot to be desired. (Ironically missing link to meta post I couldn't find about how dupes aren't bad.) – PGmath Jan 20 '16 at 14:51

2 Answers2

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Each situation really determines what you should do.

In general

  • Using generated coordinates gives you less control, but is easier.
  • Using UV's is more precise, but harder, especially on complex meshes.

Now, I will use an example scene, to show some of the differences.

In this example, we will use:

  1. Sphere one uses generated texture coordinates
  2. Sphere two uses sphere projection, to create a UV map.

In this circumstance, I like the results of sphere 1 better than that of sphere 2.

enter image description here

When using generated texture coordinates, keep in mind what mode of texture projection you are using. I have a sphere, so I am using sphere projection. For other objects with complex meshes that you do not want to unwrap, box projection is usually a good option.

When looking at the UV map that was created through sphere projection on sphere two, you may notice that the unwrap is not perfect, and that is one of the advantages of using generated texture coordinates.

Also, remember that using UV or generated texture coordinates are not the only options. Using object coordinates can come in useful when you want the texture's projection to change based on the position of the object, such as when creating roof tiles. You may use a cracked texture, and want the cracks to be in a different place per tile.

So when deciding, just think about what your goals are, and what the easiest way to get there is. In the earth model case, I would use generated coordinates with sphere texture projection.

Uncle Snail
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UV Unwrapping

The one major benefit of UV unwrapping an object is that it gives you exact control over the texture placement. Usually you would unwrap geometrically complex objects, or objects which you would like to do texture painting or add decals to.

However, UV mapping has two major pitfalls.

  • Seams. By unwrapping an object you are basically cutting it up with seams and flattening it out to place a 2D texture on it. The obvious problem is that these seams create undesirable "cuts" in the texturing. So care must be taken to place seams where they are least visible.

  • Distortion. Due to the nature of UV unwrapping, by cutting a 3D object up and plastering it flat there will be some distortion of the geometry. If done well this can be minimized fairly well, but that often requires more seams. So when UV unwrapping an object you need to find a balance between more seams and more distortion.

Usually the benefit of having complete control over the final output (which is often absolutely necessary for complex models and custom texturing) outweighs these cons. In such cases the above problems can usually be sufficiently mitigated.

Generated Coordinates

The key to generated coordinates is that they are 3-dimensional. This is both their biggest advantage and disadvantage. Being 3-dimensional makes them perfect for procedural textures and voxels (though position coordinates work just peachy too). However, being 3-dimensional also means it is often tough and/or not ideal to use generated coordinates with 2-D image textures.

There are a few ways of using generated coordinates for 2-D textures, through using different mapping projections or some more advanced vector wrangling.

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PGmath
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