Non-spatial WFS to CSV
Hi all,
Would anyone be able to suggest a workflow of exporting non-spatial records from wfs service to csv format? It is a big file with property title information (2+ million records), so I was thinking about narrowing the search by specifying Land District (GetFeature?). I did not work much with wfs services so simplified explanation would be great.
Maybe someone from New Zealand with data.linz experience, especially their wfs services?
Regards,
Maksym
I ended up running workbench with SQLExecutor, which uses required parcels an an initiator. Also I set syntax, that @kimo suggested, exposed attributes and run it through AttributeManager to retrieve duplicated values. On the output I received a table of title_no relations between two sources. It has duplicated values for title_no, as was expected.
Bruce's two workbenches do work, but for spatial layers only. They do not use CSV and they do not make a subset of non-spatial records which was the question. They also leave all field widths at 2048+ chars which will crash ArcGIS when you try to index these fields.
The problem is that there is no easy query you can do on the non-spatial tables so you have to download the whole table and make a subset using some other related spatial layer afterwards.
Trying to download very large tables with WFS is sure to end badly. My system halts suspiciously at exactly 1 M records for some layers so there is some sort of limit that I could not remove, even though LINZ says there is no limit on their part and it works for them.
For very large tables LINZ provide a changeset mechanism to just download the changes to merge into an existing table that has been downloaded previously using the zip-and-ship interface. This is quite a bit more complex but much faster in the end.
My solution is to use the HttpCaller transformer to download the changesets to a CSV file and then update a geodatabase with a predefined schema. The GML format is no better at defining field widths than CSV, both give you the field names. The advantage of CSV is that it is much more compact, human readable and flexible.
Even CSV spatial layers are able to be converted into featureclasses because the shape field is WKT format which can be transformed.
Web services are unreliable. Often you get a failure to connect, or you get an interruption. It is helpful to check if you have got the expected number of records and allow for a restart if it is not correct before you plough on and corrupt your database.lds-bde-sqlite-changeset-sample.fmw
If you use a WFS FeatureReader (instead of a Reader) then you can use any extent to download a (small!) subset of features.
An extent is supported which is usually better than an actual polygon, do a clip or select after you have reduced the features, you may want adjacent parcels.
You are correct, there is an option of exporting csv table (700+ MB) or .gdb (nearly 1GB). The idea of this exercise is to have all spatially represented parcels with title number as a reference to match the rest of the information from title memorial list (which is a non-spatial web service).
At the end I would have all required parcels (around 100 - potential subdivision) with additional information (Joined, Related?), so I could see what parcels are affected by easements etc. I can do that with ArcMap but the problem is how to query out unnecessary titles prior to bringing to ArcMap, so I would have only those that match by certificate of title number.
You would download the memorials as a gpkg, add in your 100 titles and run a workbench which started with an SQLCreator that had something like:
SELECT * from title_memorial, mytitle WHERE title_memorial.title_no = mytitle.title_memorial AND current = 'T'
Another way is to use a python script with a dictionary or set.
You will need a relate rather than a join because there will be multiple current memorials for a given title. There is a memorial_type where you could also discard mortgages etc.
Hi Maksym
MakeFeatureTypes creates a Geodatabase table handy for browsing LDS data but primarily useful for creating the picklist of available layers for DownloadFeatures, which does what it says; tables will ignore the bounding box parameter.
Output is Geodatabase.
DownloadFeatures is suitable for embedding in a ModelBuilder tool to pick up map extent, I'll make a sample when I get time.
You will need to edit the URL parameters to insert your API key.
