How do I prevent FME from correcting my gml data in the reader?

Perhaps this will work: read it as XML instead and then use a GeometryReplacer to build the geometry

You're right, it does seem to automatically fix those errors. I don't really see an easy way to not have it do that.

There is a setting on the GML Reader: Parameters -> Advanced -> Continue on Geometry error, but even if I set that to No it will fix those "small" errors. There is also an option to save the geometry fragment as a separate attribute, you could try comparing that to the resulting geometry. Something as simple as counting the number of values in the poslist there compared to the number of vertices should already give you an indication that fixes have been made.

That is a possibility, but with all the possible geometries available in GML also like a lot of work.

Do you have a sample dataset? I'm sort of surprised it happens on reading. Generally (I thought) we only make fixes like that when writing data, and only then in cases where the output would otherwise be invalid. I personally don't think we should be making changes to incoming data.

If the data is confidential then please submit it to our support team (safe.com/support) and they can query this with our developers.

Is this issue still on the radar? We are looking forward to a solution.

OK, so I've been looking into this and getting feedback from our developers.

It's working as designed, in that it was designed - rightly or wrongly - to automatically handle these issues. However, there are a few "settings" that we can tweak that will help a little.

So to explain... as I understand it, when FME reads GML data it has a specification for the GML and reads it into the translation. In my workspace it's denoted with this log message:

Using XSD semantics configuration file 
'file:///C:/Program Files/FME2019/xml/gml_v3.2/gml_config.xml'.

That's for plain GML. If I was reading CityGML instead, it would use a different file. Anyway, that specification tells FME how to handle each type of geometry. There are some settings that apply, one of which is called keep-duplicate-coordinates!

In the CityGML spec, that option is turned on by default. In the regular GML spec, it is turned off. So, I can open that file (gml_config.xml) in a text editor and make some edits.

Firstly I find this section (look for gml:pos):

               <mapping match="gml:pos">
                  <signature name="xfmap-pos-collector"/>
                  <references>
                     <macro:use name="geometry-references"/>
                  </references>                                            
                  <geometry>
                     <macro:use name="geometry-builder-coordinate-system-data"/>
                     <data name="axis-separator">
                        <literal expr="whitespace"/>
                     </data>
                     <data name="coord-separator">
                        <literal expr="|"/>
                     </data>

It starts at line 1804 in my version. Then I add three lines to turn on the option to keep duplicate coordinates...

               <mapping match="gml:pos">
                  <signature name="xfmap-pos-collector"/>
                  <references>
                     <macro:use name="geometry-references"/>
                  </references>                                            
                  <geometry>
                     <macro:use name="geometry-builder-coordinate-system-data"/>
                     <data name="axis-separator">
                        <literal expr="whitespace"/>
                     </data>
                     <data name="keep-duplicate-coordinates">
                        <literal expr="true" />
                     </data>
                     <data name="coord-separator">
                        <literal expr="|"/>
                     </data>

Now I find another section about 40 lines later (look for gml:posList)...

               <mapping match="gml:posList gmlcov:positions">                         
                  <signature name="xfmap-posList-collector"/>
                  <references>
                     <macro:use name="geometry-references"/>
                  </references>                                            
                  <geometry>
                     <macro:use name="geometry-builder-coordinate-system-data"/>
                     <data name="axis-separator">
                        <literal expr="whitespace"/>
                     </data>
                     <data name="coord-separator">
                        <literal expr="whitespace"/>
                     </data>

...and add the same setting there:

               <mapping match="gml:posList gmlcov:positions">                         
                  <signature name="xfmap-posList-collector"/>
                  <references>
                     <macro:use name="geometry-references"/>
                  </references>                                            
                  <geometry>
                     <macro:use name="geometry-builder-coordinate-system-data"/>
                     <data name="axis-separator">
                        <literal expr="whitespace"/>
                     </data>
                     <data name="keep-duplicate-coordinates">
                        <literal expr="true" />
                     </data>
                     <data name="coord-separator">
                        <literal expr="whitespace"/>
                     </data>

Now, when I run the workspace again, duplicate coordinates are kept in the data.

That setting - keep-duplicate-coordinates - is documented here: http://docs.safe.com/fme/2021.0/html/FME_Desktop_Documentation/FME_ReadersWriters/xml/xml_line.htm

You'll notice that there are two other similar settings: demote-incomplete-geometry and allow-incomplete-geometry. They're both false by default so by adding/applying those settings you would set up FME to stop auto-processing other irregularities.

There are similar settings for other geometries - for example polygons.

Now, I don't know if that will account for all of your issues. I don't see a specific setting for multiple coordinates in a point feature, and the incomplete geometry setting for a polygon will still close a polygon without a matching end-coordinate (it will only change to pass a polygon with two or fewer coordinates).

So it's not a total solution here, and applying each of these settings does involve manual editing of these setup files, rather than just turning on a parameter in FME itself. There is some effort and testing involved.

The alternatives would be:

• I file a request (with our development team) to add more settings to do what you want
• I file a request to expose these settings as parameters
• I file a request for the XMLValidator transformer to validate geometry as well as syntax/schema
• You set up a solution that ignores these settings. It would need a workspace created to read the GML file (using a textfile reader to preserve the original content) and to parse the content to look for issues. I can see this being a worthwhile project, but perhaps not one that you want to embark on.

Obviously me filing a request doesn't necessarily guarantee if it's going to get implemented, or when. So that's more of a long-term strategy.

I hope this is of some use. Let me know if you need further help with the settings above, or trying one of the alternative solutions. I'll also suggest that you contact my colleague Dean through the support team (safe.com/support) if you get really stuck. He's our XML expert and he may have other insights that I don't.

Regards