What are ADE Project Files and why do we have them?
You will see references to ADE project files in many places in ADE, on the forum and in the documentation. With the introduction of project specific settings it is important to understand what a project is.
What is an ADE project?
A project can be defined as a piece of work that has a specific purpose (such as to find information or to make something new) and that usually requires some planning and may take a long time to complete. In ADE this piece of work is specifically about creating a new airport for the flight simulator or modifying an existing one.
In ADE this work is stored in a project file. There is one project file per project so in that sense the term project and project file are synonymous. Each project file contains the information needed to create a new airport or modify and existing one. It is not possible to have more than one airport in a project file or to have a project file that does not contain an airport. Project files store the information about the airport in a special format that is understood by ADE but not by any simulator. Over the life of ADE the project file format has changed and there are a number of different extensions:
ade, ad2, ad3 and ad4
The current format is ad4 and this is the one that current versions of ADE will save. It is possible to load the other project file formats into ADE but not save them in the old format. Generally each format has provided the ability to store more information or load and save that information faster.
Why do we have a special format?
In other airport editors such as AFCAD or AFX there is no project file and everything is handled in the bgl file format that FS understands. So why don't we? Wouldn't it be simpler all round to just use the bgl format?
Well it might appear simpler to just load and save your project in the Bgl format. However there are issues with that. Repeated loading and saving has been know to cause coordinate drift in object locations due to rounding errors. There are also several types of Bgl formats created by different compilers and used for different purposes such as terrain, airports, group polys and so on. So it isn't possible to put everything into one bgl file. There are also things which we might want to use like that either cannot be represented in the Bgl file format or which we don't want to be shown in the simulator. Finally we might want to store information about objects like when they were last changed and that is not possible with the Bgl format either
For example ADE makes a lot of use of background images, guidelines, helper shapes and so on. These can't be represented in a bgl file and we probably would not want our guidelines and other helpers showing up in the sim in any case. ADE has an approach editor and to make this possible it loads and stores information about a lot of navaids. Although these could be compiled into the bgl file we would not want to be duplicating navaids and way points over a lot of different files in the sim.
So that is why we have a special project file format for ADE projects. As a rule you should never load and save your work in the bgl format because you will lose a lot of information along the way.