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Tabular Interface

using ArchGDAL; AG = ArchGDAL
using DataFrames

ArchGDAL now brings in greater flexibilty in terms of vector data handling via the Tables.jl API. In general, tables are modelled based on feature layers and support multiple geometries per layer. Namely, the layer(s) of a dataset can be converted to DataFrame(s) to perform miscellaneous spatial operations.

Conversion to table

Here is a quick example based on the data/point.geojson dataset:

ds = AG.read("data/point.geojson")
DataFrame(AG.getlayer(ds, 0))

To illustrate multiple geometries, here is a second example based on the data/multi_geom.csv dataset:

ds = AG.read("data/multi_geom.csv", options = ["GEOM_POSSIBLE_NAMES=point,linestring", "KEEP_GEOM_COLUMNS=NO"])
DataFrame(AG.getlayer(ds, 0))

Conversion to layer

A table-like source implementing Tables.jl interface can be converted to a layer, provided that:

  • Source contains at least one geometry column
  • Geometry columns are recognized by their element type being a subtype of Union{IGeometry, Nothing, Missing}�
  • Non geometry columns must contain types handled by GDAL/OGR (e.g. not Int128 nor composite type)

Note: As geometries and fields are stored separately in GDAL features, the backward conversion of the layer won't have the same column ordering. Geometry columns will be the first columns.

df = DataFrame([
    :point => [AG.createpoint(30, 10), missing],
    :mixedgeom => [AG.createpoint(5, 10), AG.createlinestring([(30.0, 10.0), (10.0, 30.0)])],
    :id => ["5.1", "5.2"],
    :zoom => [1.0, 2],
    :location => [missing, "New Delhi"],
])
layer = AG.IFeatureLayer(df)

The layer, converted from a source implementing the Tables.jl interface, will be in a memory dataset.
Hence you can:

  • Add other layers to it
  • Copy it to a dataset with another driver
  • Write it to a file

Example of writing with ESRI Shapefile driver

ds = AG.write(layer.ownedby, "test.shp", driver=AG.getdriver("ESRI Shapefile"))
DataFrame(AG.getlayer(AG.read("test.shp"), 0))
rm.(["test.shp", "test.shx", "test.dbf"]) # hide

!!! warning As OGR ESRI Shapefile driver does not support multi geometries, the second geometry has been dropped !!! warning As OGR ESRI Shapefile driver does not support nullable fields, the missing location has been replaced by ""

Example of writing with GML driver

Using the GML 3.2.1 more capable driver/format, you can write more information to the file

ds = AG.write(layer.ownedby, "test.gml", driver=AG.getdriver("GML"), options=["FORMAT=GML3.2"])
DataFrame(AG.getlayer(AG.read("test.gml", options=["EXPOSE_GML_ID=NO"]), 0))
rm.(["test.gml", "test.xsd"]) # hide

Note: OGR GML driver option EXPOSE_GML_ID=NO avoids to read the gml_id field, mandatory in GML 3.x format and automatically created by the OGR GML driver