hexagon logo
Register Sign in
  • Replies 15 replies
  • Subscribers 223 subscribers
  • Views 240 views
  • Users 0 members are here
Options
Related

Surface Profile - Iterate and Repierce function

DaSalo
Can someone give me a rundown of what the iterate and repierce function does? I turn it on and all of a sudden my surface profile improves significantly. Is that real?

On a similar topic, has anyone else had trouble with vector least square best fit causing a best fit error? I have had several parts now that had profile dimensions set to vector best fit, which runs fine offline, that have given me best fit errors at the end of the program. If I hunt down the offending dimension and change it to least squares the error goes away immediately. I have also had a similar problem if I set the iterate and repierce function with too small of a tolerance. I'm using an .039 (1mm) ruby and have found I need to set the repierce tolerance to at least .025 to reliably run through the program without any best fit errors. This seems to be related to features with very large radiuses of contour (almost flat, but not quite). My assumption is that the math runs out to too many decimal places and it can't handle it.

Thanks for any advice. I am inspecting a part that is just one giant contour, no flats at all, and need to have all of my ducks in a row around how all of the surface profile options work.
Parents
  • A big problem with iterate and repierce, at least in the versions I tested, is that it will actually drop points from your measured points set if they fall off the surface during the iteration. It is quite possible that these points could be the points with maximum deviation so when you see your results improve it could be that it is simply because a sort of edge filter has been applied that has trimmed off the end points as the algorithm seeks a solution that is best for the majority of the points in the set. This is the same behavior that happens if you have a scan that runs off the defined surface: it tells you that nominals could not be found for some points and then asks if you want to delete them. The difference is that with iterate and repierce I don't believe it tells you that it is doing it. It has been a long time since I tested this function so please verify this on your own.

    Once you run iterate and repierce there is no going back. If it drops measured points you can not recover them. This aspect of the functionality is the primary reason why I cut this tool from my box. I can see a path to safely using it if some scripting is applied before hand. If you write a script to pull the points from a scan and stuff them into another scan feature you can then perform the iterate and repierce on this second scan feature without risk of losing your original measured data. You will then have the ability to compare the two points sets and validate exactly what is happening with the iterate and repierce.

    My general conclusion when I last tested this was that it has good potential for post processing data on certain problematic parts that might otherwise be scrapped but had too many pitfalls for general production use.
Reply
  • A big problem with iterate and repierce, at least in the versions I tested, is that it will actually drop points from your measured points set if they fall off the surface during the iteration. It is quite possible that these points could be the points with maximum deviation so when you see your results improve it could be that it is simply because a sort of edge filter has been applied that has trimmed off the end points as the algorithm seeks a solution that is best for the majority of the points in the set. This is the same behavior that happens if you have a scan that runs off the defined surface: it tells you that nominals could not be found for some points and then asks if you want to delete them. The difference is that with iterate and repierce I don't believe it tells you that it is doing it. It has been a long time since I tested this function so please verify this on your own.

    Once you run iterate and repierce there is no going back. If it drops measured points you can not recover them. This aspect of the functionality is the primary reason why I cut this tool from my box. I can see a path to safely using it if some scripting is applied before hand. If you write a script to pull the points from a scan and stuff them into another scan feature you can then perform the iterate and repierce on this second scan feature without risk of losing your original measured data. You will then have the ability to compare the two points sets and validate exactly what is happening with the iterate and repierce.

    My general conclusion when I last tested this was that it has good potential for post processing data on certain problematic parts that might otherwise be scrapped but had too many pitfalls for general production use.
Children
No Data
© 2024 Hexagon AB and/or its subsidiaries. Privacy Policy | Cloud Services Agreement