I am currently learning to use Oresium. I notice that the oreczml-core (oreczml-core-1.0.0.jar) library is incomplete. I found out about this while trying out the examples provided in gitlab. For example, in the package org.orekit.czml.object.primary, there are missing subdirectories, such as entities, covariance, pointing, etc. Due to this problem, I could not import classes/functions such as Spacecraft, which is used in one of the examples.
What I have in mind is recompiling or update the current jar file from the available source. However, I am currently a beginner in Java programming, so I have no idea. Is there a solution to this problem?
This behavior is expected. OreCZML has evolved significantly since the 1.0 release, and many packages and class names have changed over time.
In particular, the Spacecraft class you are referring to did not exist in version 1.0 — it is a later rename/refactor of the Satellite class. This is why you cannot find it in oreczml-core-1.0.0.jar, and why some of the examples no longer match the released JAR.
The recommended solution is to use a more recent snapshot version of OreCZML built directly from the current source code, rather than relying on the 1.0 release. You can obtain this by building the project from the develop branch.
If you are new to Java, building the project from source using Maven may require a bit of initial setup. Are you familiar with Maven?