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Screensize: 640 x 480 800 x 600 1024 x 768 1280 x 1024 UserName: Password: Anti-Spam Code: Format Mode: Basic  Help  Prompt  Format: Font Andale Mono Arial Arial Black Book Antiqua Century Gothic Comic Sans MS Courier New Georgia Impact Lucida Console Script MT Bold Stencil Tahoma Times New Roman Trebuchet MS Verdana   Size 1 2 3 4 5 6   Color Black Red Yellow Pink Green Orange Purple Blue Beige Brown Teal Navy Maroon LimeGreen Message: * HTML is OFF * Forum Code is ON Smilies [quote][i]Originally posted by JosefL[/i] [br]Origin Ver. and Service Release: OriginPro 9.1 OG (64-bit) Operating System: Windows 7 Enterprise Hello dear Origin-Community! Actually I'm working on an implicit fitting function for a sphere. [b](f = (x-x0)^2+(y-y0)^2+(z-z0)^2-R^2)[/b] I wrote a very simple "Parameter Init" in form of x0 = max(x_data); y0 = max(y_data); R = 5000; z0= 5000; Due to the implicit form I have to use the orthogonal distance regression. The value 5000 is a result of already observed measurement values and also the problem I'll need help with. The max data for x and y works quite fine as a result of the Situation in the coordinate Systems. Depending on what value I choose (3000-7000) for R and z0 (same as R due to surface conditions) the result of the fit shows very different results. None of the variables is allowed to be fixed and so this might be the first problem. Also the surface of the measurement values could be a reason for the instability of the results. Compared to a radius of about 7 meters (for the fitted sphere) the measurement surface is just 15 mm x 15 mm.... Hopefully someone has the idea to solve my problem and bring some stability to the resulting parameters of the implicit fitting function. Kind regards, Josef [/quote]   Check here to include your profile signature. Check here to subscribe to this topic.