Understanding Zoom Levels for orthophotos.

And what to use, why, and where!

Using Ortho4XP, you can cover large areas of the scenery with beautiful orthophotos, giving you a more realistic view of the world as you fly. But there a caveat, or two.

First of all takes a lot of space. Looks that you might need the hard drives from all the world to fit in those you need!

Second, need more space in you RAM/VRAM and stresses your computer resources and abilities! Lets see them, one by one.

What a Zoom Level is

Zoom Level (ZL) is, as it is obvious, how zoomed the the aerial view is towards the ground. The higher the zoom level is the more zoomed the images is. Or with another perspective, how resolution is each level given a standard view from the camera. Actually there are a lot of maths behind this but this is the general idea; the higher the ZL is the more resolution we will get.

There is a algebraic relationship between ZLs and we must be aware of it. One level higher ZL, covers the 1/4 of the lower ZL area. In other words, you need 4 textures to cover the same area as before. The image below indicates the relationship (the number are not real, just for indication purposed, take in mind the assumptions in the next paragraph).

How storage space do they need.

We will start with some “given assumptions” to make things easy to understand.

  • Start at ZL 15 and go higher. Below this level, things do not look so nice.
  • Each texture is size 4096×4096 and at ZL15 covers 1 square kilometer.
  • The size of this texture is 10 MB (megabytes)

Take in mind all the above, then to cover the same 1 square kilometer area we need storage, depending Zoom Levels:

  • ZL15 – 1 texture = 10 MB
  • ZL16 – 4 textures = 40 MB
  • ZL17 – 16 textures = 160 MB
  • ZL18 – 64 textures = 640 MB
  • ZL19 – 256 textures = 2560 MB – 2.56GB
  • ZL20 – 1024 textures = 10240 MB – 10.2 GB

As you can see, very quickly, the amount of storage is getting ridiculous huge! But the good thing is that we do not need to go high ZL, at least not everywhere.

If your are flying mostly airliners, then you only are close to ground when you are at the airport, during takeoffs and landings. So having huge areas covered with i.e. ZL18 is not useful at all. You can get away even with ZL15! Don’t believe it? In the image below, I’m flying at 6,500 ft and the area below is covered with ZL15 orthoimagery! (for full resolution click the here)

Memory issues! ?

One other aspect of the orthophoto usage is that you need more RAM (and VRAM) than the default scenery. Actually with 16 GB of RAM, on high settings, you might find yourself in a critical situation, where you RAM might not be enough. As X-Plane loaded the scenery in 1×1 degree tiles around you, loads all textures for tiles in your RAM and then depending on your position, are loaded into VRAM. As you can understand, having less textures to load, you will have better performance and avoid reaching your hardware limits, because then you get low fps and eventually stutters!

A proposal for optimizing your orthophotos coverage

  • First of all, adjust Ortho4XP setting, so you get higher ZL for the airports. ZL 18 for airports gives perfect results and performance. Extra tip: Use apt_smoothing_pix 32. Makes airport runways and around areas curve very nicely.
  • If there are areas that you might do VFR flights, or have some special interest to you, use ZL 16.
  • I suggest ZL 17 only in a very few selected areas that might you want to do low level, or helicopter flying.
  • Use ZL 15 for the rest of the world! OK still in ZL15, the whole world will require ridiculous amounts of storage, but where you will fly! Also using ZL 15 will reduce (a lot) the download times!

Epilogue

Orthophotos offer a great opportunity to enhance X-Plane’s visually for free. By optimizing the Zoom Level you can get both great visual, and good performance, while minimizing the amount of storage required.

Go to youtube and search for “Ortho4XP tutorials”. You will find a ton of them, in almost every language, and will also provide you with some more advance tips, like selecting manually some areas where you want higher resolution.

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