There are many things going on, let me explain
At the beginning Telescopius used the nova.astrometry.net API to request plate solving of all pictures, but some shortages on their service, some delays in many cases due to job queues, and their suggestion to run plate solving on our own servers to avoid waiting for their global queue, made me switch the implementation to have it running on our own server.
Plate solving works by using index files containing the position of stars. Nova uses a set of index files unavailable to the general public due to licensing issues (they are called the “200-series”), while our server uses a different set of index files which naturally gives different results. They offer 2 or 3 different sets of index files, I’ve tried them all and none of them solves difficult pictures the same way with the default settings.
I estimate over 95% of all deep sky pictures get correctly plate solved on Telescopius. When I noticed some images were being plate solved on Nova but not on Telescopius, I started trying different settings but none of them would work in 100% of the cases. I would really love to have the same index files because I’m not sure if the reason they are failing is because of the settings, the index files, or… hardware.
Index files are over 20GB. Some times the jobs time out before trying all index files due to memory constraints. I need to upgrade the system to have more memory but the current hosting is quite expensive. Given that about 95% of pictures get plate solved correctly, paying double or triple for the hosting service just to try to get the extra 5% solved didn’t make much sense, but I’m planning to migrate to another cheaper hosting to see if we can improve that number. Another idea is to try nova.astrometry.net only for failed pictures.
I’ll keep working on improving the success rate of plate solving. In the meantime, for pictures which don’t get plate solved blindly, you can add hints next to any one of the revisions (all revisions of a picture share the same hints) by clicking on the drafting compass icon:
Entering the coordinates or just the FOV usually helps a lot because it reduces the number of index files to search in. I hope this helps!