Change detector attribute no matching problem
Hi everyone,
I am using a ChangeDetector, only on one attribute "parcelle", to compare differences between polygon layers, but there is a problem because all of the polygons are detected as "changed" (then they should not, because values of "parcelle" attributes are the same in the two layers) :
Port 1 (Added) :
Port 2 (Deleted) :
I thought that the problem was because of the encoding of these attributes. So I have tried to use the AttributeEncoder Transformer, but it changes nothing :
I also have tried a FeatureMerger on these attributes and it works.
Thank you.
Aurélien
Hello @arxit,
Are you able to attach your workspace or a sample of the data(1feature from each source to an FFS file would work)?
Secondly, on one of the images, 'pict-1.png' it almost appears that there is whitespace at the end of the value so rather than '1391' it looks like it could be '1391 '. Are you able to just verify this? I think I may just be seeing things/stretching it.
As suggested by mark_1spatial, I have test only one polygon and i have removed all attributes except "parcelle".
I inserted loggers (in attachments : script-log.zip), two after my sources and two after ChangeDetector (in outputs).
I'm sorry about the simplicity of this problem.
Try inserting a StringFormatter with the format string "s" (only the letter s, no quotes) on both datasets entering the ChangeDetector:
You could also try inserting an AttributeTrimmer as well, in case there are any spaces or non-printable characters.
I was not able to reproduce the issue using FME 2017.1.
I've had some interesting challenges with the ChangeDetector/UpdateDetector in the past.
To debug I suggest you use a Tester to only allow through one equivalent polygon from each stream, then remove all the attributes except the one your are testing against. Then check the results. If it works OK then start to isolate the problem by allowing attributes through.
Alternatively can you post a screen capture of the two relevant features (using Run with Breakpoints) just before they enter the ChangeDetector.
Finally, post the data with a small sample. You can use the Recorder transformer to create an FFS file that you can upload.
Try temporarily replacing the ChangeDetector with a FeatureMerger, merge on "parcelle". If the behavior is the same, I pretty much guarantee that the problem is with the features themselves and not a bug with FME.
You could also consider posting a small sample dataset here that exhibits the problem, that would be very helpful.
In the change detector are you matching geometries as well as attributes?
Have you verified for precision differences? Try inserting a CoordinateRounder to 3 decimal places on both datasets before the ChangeDetector.
