Approach

There does not appear to be a way to hook directly into the internal texture loading mechanism of X-Plane via plugins. Instead, this project acts as a virtual file system interface for orthophoto satellite imagery.

As needed, imagery is downloaded from the indicated satellite photo sources as areas are requested. Imagery files are detected by naming convention of {row}_{col}_{maptype}_{zoomlevel}.dds This is the standard convention for imagery created from Ortho4XP.

How does X-Plane access scenery?

Let's look at how X-Plane accesses scenery. In the install directory of X-Plane there will be a Custom Scenery folder. Under this folder there will be a number of sub directories of scenery and a scenery_packs.ini configuration file. This is where X-Plane will look for scenery.

Under each scenery subdirectory, there will be an Earth Nav Data directory that contains a number of lat-lon named subdirectories. Under these subdirectories will be a number of DSF files that contain instructions for X-Plane for this set of coordinates.

These DSF files are picked up by X-Plane based on the area that you are flying. During flight initialization a set of these files around your takeoff location are loaded. While flying new DSF files will be loaded. This loading while flying happens asynchronously behind the scenes.

The DSF files can contain various instructions for X-Plane. What we are interested in for orthophotos are terrain files. The terrain files a DSF contains would then point to the textures requested for this terrain, including satellite photo textures. These files are typically .dds files, though that's not always the case.

DDS files can contain multiple copies of the same texture at reduced resolutions. These are referred to as 'mipmaps'. This allows X-Plane to just pull in the minimum amount of data that is required into memory at any given time. Typically the maximum resolution for a texture is only required while flying low and for close by tetxures.

How this project leverages this setup (high level description)

This project effectively requires all the parts of normal orthophoto satellite imagery, except for the satellite photos themselves.

Existing mechanisms to create and manage DSF files, and related terrain files, still applies. X-Plane continues to reference these files as per normal.

This program will detect when DDS files are accessed and read from X-Plane. When X-Plane attempts to read a specific mipmap of a texture this program will pull down just the minimum required data and return this data to X-Plane. This happens behind the scenes and as far as X-Plane is concerned, it is continuing to read a normal filesystem.

Since we only download the minimum required data, this process is relatively efficient.

Data is cached in memory until a memory limit is reached, at which time older data will be purged.

Expert Usage and Overriding Defaults

Warning

I highly recommend using the pre-packaged scenery packs provided with this tool.

However, it's entirely possible to use your own scenery, if you wish. This could be useful for situations where you want an area I haven't gotten to packaging yet, or want a different zoom level that what is provided.

This should be considered an experts-only feature though and assumes: * You are very comfortable with the command line * You are very experienced using Ortho4XP and with installing custom scenery * You are very familiar with filesystem concepts and managing your Operating System

If you don't have this experience, that's okay, but likely you will struggle adding your own custom created scenery. I would recommend that you familiarize yourself with each of these listed items before proceeding.

Adding your own created sceneries

Ready to add your own sceneries? Great!

So as mentioned above, this tool effectively overrides the 'textures' directory that XPlane is pointing to in order to location satellite imagery that is referrenced by a scenery pack's terrain files.

Due to how XPlane identifies terrain information, these directories have been split up into reasonable sized pieces, which is why each provided scenery pack has numerous numbered directories.

This project creates a special pass through filesystem that mounts directories into a location that XPlane can find and intercepts requests to '.dds' files. This is handled through the magic of FUSE (Filesystem in UserSpacE). FUSE is a common and standard feature of Linux, but requires extra stuff for other Operatings Systems.s

Sceneries stripped of satellite imagery, likely still have coastline PNG files that must be preserved. These are simply passed through when requested.

You can take advantage of this setup for your own scenery that you have packaged: * Place your scenery directory in Custom Scenery/z_autoortho/scenery

When execute Autoortho will detect directories in that scenery dir and mount these in your configured Custom Scenery directory.

Ortho4XP Usage Tips

Ortho4XP can generate scenery files without downloading photos, which is perfect for this project. In the config set skip_downloads to True

Since this starts with low resolution imagery until you get going, I recommend enabling high_zl_airports

So far I've been testing with a ZL of 16 for most tiles with increased ZL of 18 for airports. You may have want to play around with the ZL levels for best results.

Higher zoom levels will lead to increased resource usage and longer delays initially starting up flights.