Thank you for your reply and file.

I have already figured this out.

Just created a new column with linear time values, ran a match with the existing non linear values, copied the values that were missing in the first place to the existing time column and reordered. That gave me the xyz coordinates distributed along a linear time value.

Blank rows are just fillers for keyframes with no spatial information, they are not actually blank, they have time information which is essential to get the correct speed of the object. The animation software interpolates the missing position coordinates. Now the speed is correct and it's running smoothly.

Yes, 500k rows amount to a lot of time but I can't drop any data, I must have the possibility to change speed at any time without loosing detailed information. But that's an animation detail that I can easily deal with.

Kind regards,

Rui