DPlot

I've been plotting some large data files (600,000 points) and have been having a hard time deleting some of the aberrant data. It is easy to see graphically, but almost impossible to delete from the original data. The faulty data is very different from the real data, but is intermixed with real data points. The aberration isn't just noise, it's a large spike in the data. The capability to graphically select and delete data points would be very nice. If there is another method for accomplishing this, I'd love to hear it. Thanks. -Rich Forrest

Two things to look at: Edit>Filter, under "Filter type" choose "Random spike removal". Click the "Help" button for a description of what DPlot considers a random spike.

If you don't have a very large number of points to delete, the "Edit Mode" button should be useful (11th button from the left). You can click on your "bad" data points and delete them. With 600,000 points you'll likely need to first zoom in.

Thanks, your suggestions helped quite a bit. The random spike removal doesn't really work for me. My data values don't have constant spacing. Is there a way to filter the data without having constant spacing? Also, the edit mode button works great, but it would be nice if I could draw a box around the points I want to delete. This would facilitate the deletion of large numbers of points.

Also, a second question about specifying extents in the options menu. Sometimes I specify an extent, but DPLOT does not use the value I chose. Any ideas? Thank you very much for your help.
-Rich Forrest

Rich,

Thanks, your suggestions helped quite a bit. The random spike removal doesn't really work for me. My data values don't have constant spacing. Is there a way to filter the data without having constant spacing?

I should relax that requirement for the random spike removal. For the other filters... constant spacing isn't mathematically a requirement, but the operations don't do what you intend for them to do (remove a frequency band, for example) unless the spacing IS constant. Really the random spike removal is a bit out of place here; I'll most likely make that a separate menu command, along with allowing you to enter a parameter or two that helps define what a spike is.

Also, the edit mode button works great, but it would be nice if I could draw a box around the points I want to delete. This would facilitate the deletion of large numbers of points.

I'll add this one to the to-do list. Again, this will probably be a separate function on the Edit menu... "Delete points within box" or something like that.

Also, a second question about specifying extents in the options menu. Sometimes I specify an extent, but DPLOT does not use the value I chose. Any ideas? Thank you very much for your help.

You most likely have "Auto-tick marks" checked under Tick marks. In other words you're allowing DPlot to pick a tick mark interval. OR you have "Specify interval" checked, but the extents you've specified aren't a multiple of that interval. In the former case, this paragraph from the Help file explains the problem:

"The actual coordinates of the corners may not turn out to be exactly the same as those you have specified. DPlot will adjust the extents such that the resulting tick mark intervals are multiples of 1, 1.5, 2, 2.5, 3, 4, 5, 6, or 8 times a power of 10."

The gyrations DPlot goes through to pick a tick mark interval when you have "Auto-tick marks" checked is too wordy to mention here. The short version is - if the actual extents are important to you, you should also use "Specify number" or "Specify interval" under "Tick marks".