Hello! Have you seen the thread on contributing graphics to the pakset? You can read it here
. It is the best place to start.
In summary, graphics are produced using the free and open source 3d editor Blender
. They are then rendered using certain automatic settings (a Blender script, which you can download, for rendering and camera and render setups that are best derived by adapting existing Blender models, the sources for many of which are available from links in the thread that I linked above).
Finally, the graphics from Blender are collected together in a single image using a program called “Image Masker” (written specially for Simutrans) and then the .dat files are written to go with it, before packing them into the pakset objects using the Simutrans makeobj.
(If you have any questions about this process, please ask it on the thread linked above after you have read the relevant parts of that thread, as it would be duplicative to discuss that in detail here).
The easiest way to start making objects for the pakset is to practise first by making small variations on existing objects. Aircraft are quite hard to do compared to some others, so you might find it easier to start with one or two practice projects first, such as some houses, shops, or perhaps some road or rail vehicles. Once you get used to that, you will then find it easier to do the slightly more difficult things such as aircraft than if you start with aircraft straight away.
It is quite tricky to get the scale right with aircraft, as they are all to a slightly different scale depending on their size (if they were all made to the same scale, the biggest ones would be too big to fit inside even a 255x255 sized tile, the maximum that can be accommodated in Simutrans). Note that larger aircraft have the complication of having a larger tile size than the base pakset tile size of 128x128, but this can be dealt with by using a .blend file of an aircraft of similar size as a template.
I hope that this is helpful – happy graphics making!