# Why does the solve error keep changing?

I've been doing a simple camera track, I placed 8 markers and thought now is a good time to see what the solve error is: 11.4301

The confusing thing is, that if I press Solve Camera Motion repeatedly I keep getting different solve errors, even though I have changed absolutely nothing since the last time I did a solve.

Am I doing something wrong? It doesn't seem correct to me, surely whatever algorithms are running to do the solve won't change after each click without me influencing it in some way.

• Yes, sometimes solving the scene again yields different error numbers, I'm not sure if previous solution is taking into account on a new one... Not really an answer as to why, but since you have the "Keframe" box checked on the Solve tab, Blender is probably giving the trackers different weight in the solution. From the Wiki: "Automatic Keyframe Selection Added an option to select keyframes used for initial reconstruction automatically (r57133). This option enables some fancy math algorithms which tries to find a keyframe pair with minimal reconstruction error and best scene scale guess. " – cegaton Jul 3 '14 at 0:10
• wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.68/… – cegaton Jul 3 '14 at 0:10
• Thanks for your reply, if this is the intended behaviour then it is problematic for the following reason. My initial solve error was not the best one i could achieve, does this mean users are supposed to keep solving in with possibility of achieving better results? I managed to get it to 3 from 11 without any changes at all, and this was without any further refinement of focal point etc. – Neil Jul 3 '14 at 6:18
• @AnsonSavage For the lens distortion see this answer: blender.stackexchange.com/questions/15620/how-to-tweak-k1- k2-and-k3-undistortion-values-in-motion-tracking for the lens you ahve to do a bit of research on what lens and sensor your camera uses or use this app: play.google.com/store/apps/… .... please read blender.stackexchange.com/questions/16131/… and for other questions please make a new post – cegaton Nov 14 '15 at 4:28
• @AnsonSavage what I did was simply set the refine option right above the solve button to "focal length, k1, k2", which means it will try to guess the focal length and distortion automatically. Or, if you use the trick to find distortion that cegaton provided above, but you still don't know the focal length, you can set refine to focal length only – markasoftware Dec 6 '15 at 5:34