[gdal-dev] OGR Field Types?

[Even Rouault]

Le vendredi 22 mai 2015 00:33:43, Stefan Keller a écrit :
> 2015-05-21 23:34 GMT+02:00 Even Rouault <even.rouault at spatialys.com>:
> ...
> 
> >> 4. "Geometry(Easting)","Geometry(Northing)"
> > 
> > For points only I guess?
> 
> Yes.
> 
> >> 5. "Geometry" -- encoded in WKT; having subtype values WKT (default),
> >> Point, LineString, Polygon.
> > 
> > "WKT" is not really consistant with Point,LineString,Polygon since the
> > later would be expressed as WKT I guess. So perhaps WKT, WKT(Point),
> > WKT(LineString), WKT(Polygon) ?
> 
> Right, d'accord. So, let's introduce following two geometry types:
> * "Easting","Northing"
X,Y or Geometry(X), Geometry(Y) or Point(X),Point(Y) would perhaps be easier 
to get. I don't know.
> * WKT, WKT(Point), WKT(LineString), WKT(Polygon)
> 
> There are additional restricions to these geometry types:
> * "Easting","Northing" must co-occur and should be neighboring columns
> (in either order).
I guess most people would do that, but I don't see a strong rationale to 
impose neighboring coumns
> * if WKT is given, all rows are expected to contain the same geometry type.
For generic WKT, all geometry types should be possible (as currently). Only 
for WKT(xxxx), geometries should be restricted to the specified type.
> * There's only one geometry column per .csvt, namely either
> <<"Easting","Northing">> or <<WKT>>.
Kind of makes sense for Easting,Northing. But for WKT columns I don't see a 
reason for such a restriction. Actually there's already a 
secret/undocumented/debug mode in the CSV driver to read multiple geometry 
columns (I won't reveal it unless I'm tortured, but you can look at the code). 
This was mostly useful at the first stages when developing RFC 41.

> 
> OK?

Not sure what kind of committment would be expected if I say "OK", so I'll 
abstain ;-)

> 
> --S.
> 
> 2015-05-21 23:34 GMT+02:00 Even Rouault <even.rouault at spatialys.com>:
> > Le jeudi 21 mai 2015 23:17:26, Stefan Keller a écrit :
> >> Hi Even
> >> 
> >> I just see some type mod and subtype definitions for .csvt files in
> >> the CSV docs [1] :
> >> <<
> >> In a single line the types for each column have to be listed with
> >> double quotes and be comma separated (e.g., "Integer","String"). It is
> >> also possible to specify explicitly the width and precision of each
> >> column, e.g. "Integer(5)","Real(10.7)","String(15)". The driver will
> >> then use these types as specified for the csv columns. Starting with
> >> GDAL 2.0, subtypes can be passed between parenthesis, such as
> >> "Integer(Boolean)", "Integer(Int16)" and "Real(Float32)"
> >> <<
> >> 
> >> Following questions and suggestions about .csvt:
> >> 1. Do type names really have to be in double quotes?
> > 
> > No
> > 
> >> 2. Is the separator always comma or can it also be a semicolon?
> > 
> > Yes, always comma
> > 
> >> 3. What about a Geometry type with subtypes? I suggest to add
> >> 4. "Geometry(Easting)","Geometry(Northing)"
> > 
> > For points only I guess? Well you can build points with a OGR VRT from 2
> > CSV columns. I might perhaps add in some time an open option to specify
> > the columns for the easting/longitude and northing/latitude.
> > 
> >> 5. "Geometry" -- encoded in WKT; having subtype values WKT (default),
> >> Point, LineString, Polygon.
> > 
> > "WKT" is not really consistant with Point,LineString,Polygon since the
> > later would be expressed as WKT I guess. So perhaps WKT, WKT(Point),
> > WKT(LineString), WKT(Polygon) ?
> > 
> >> What do you think?
> >> This could also make QGIS "Add Delimited Text Layer..." even better.
> >> 
> >> --S.
> >> 
> >> [1] http://www.gdal.org/drv_csv.html
> >> 
> >> 2015-04-29 22:57 GMT+02:00 Stefan Keller <sfkeller at gmail.com>:
> >> > Salut Even,
> >> > 
> >> > Merci!
> >> > 
> >> > 2015-04-29 20:35 GMT+02:00 Even Rouault <even.rouault at spatialys.com>:
> >> >> Stefan
> >> >> 
> >> >>> Questions:
> >> >>> 1. How is 'binary' encoded? E.g. when defining binary in a CSV file,
> >> >>> how is it encoded? Hex?
> >> >> 
> >> >> There's no support in the CSV driver for binary data
> >> >> 
> >> >>> 2. Can a field in a CSV input files have a IntegerList or a Binary?
> >> >> 
> >> >> No. Well on writing, the IntegerList will be serialized as a string.
> >> >> But not recognized as IntegerList on reading
> >> >> 
> >> >>> 3. What is the value delimiter in a field of type IntegerList,
> >> >>> Integer64List, RealList, StringList?
> >> >> 
> >> >> The default serializatoin will be
> >> >> (number_of_elements:val1,val2,...,valn), but currently it is
> >> >> truncated to 80 chracters
> >> >> 
> >> >>> 4. "Boolean, Int16, Float32" are mentioned as subtypes. Are there
> >> >>> more subtypes?
> >> >> 
> >> >> Not currently. See
> >> >> https://trac.osgeo.org/gdal/wiki/rfc50_ogr_field_subtype
> >> >> 
> >> >> Even
> >> >> 
> >> >> --
> >> >> Spatialys - Geospatial professional services
> >> >> http://www.spatialys.com
> > 
> > --
> > Spatialys - Geospatial professional services
> > http://www.spatialys.com

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