During the OGC Code sprint we worked on JSON-FG example datasets. These datasets touch on the various specific topics of JSON-FG, such as inclusion of geometry with CRS other than WGS'84 in the place member, temporal information in the time member and 3D geometries.
We created 6 JSON-FG example datasets:
-
current topographic BGT features
-
current and historic topographic BGT features
-
Dutch municipalities from 2003
-
Buildings as 3D Prims
-
Buildings as Polyhedrals
-
Circular arc interpolation
We used the GDAL draft implementation to convert from GPKG, PostgreSQL or GML files to JSON-FG. All objects in the example datasets intersect with the bounding box of the buffer of 200 meters around ‘Het Binnenhof’ in The Hague.
We will describe each dataset hereafter.
Goal
With this example file we want to demonstrate the inclusion of geometries in an CRS other than WGS'84. The JSON-FG draft specification requires that geometries with a different CRS must be included in the place member, and that geometries that are valid GeoJSON geometry types in WGS’84 must be included in the geometry member.
The specifications also allow to include both GeoJSON geometries in WGS'84 in the geometry member, and the geometries in RD in place member. The advantage is that the JSON-FG can also be read in a GeoJSON client. The disadvantage is increasing the file size (and payload).
Process
We retrieve a full download of the BGT including history from PDOK.
The complete BGT file from PDOK is filtered for the topographical objects without an end time (eindregistratie IS NULL). The example datasets therefore describes the current situation of the position in the LV-BGT on a reference date around the end of October (last LV publication date:: lookup?).
All geometry types in the file, expressed in WGS'84, are also valid GeoJSON geometries.
We create two example datasets with the GDAL draft implementation:
- a dataset with only BGT features in RD in the place member
- a dataset with geometry in WGS'84 in the geometry member and geometry in RD in the place member
Result
We drag-and-drop the JSON-FG file with geometries in the "geometry" member in QGIS. See result below.
{
"type": "Feature",
"featureType": "paal",
"coordRefSys": "[EPSG:28992]",
"properties": {
"lokaalid": "G0518.1e0a6f158f7be183e053530a0b0a8a7d",
"objectbegintijd": "2015-08-17",
"tijdstipregistratie": "2015-08-17T14:26:33Z",
"lv-publicatiedatum": "2018-06-21T16:17:38Z",
"bgt-type": "niet-bgt",
"plus-type": "afsluitpaal",
"hectometeraanduiding": null
},
"geometry": {
"type": "Point",
"coordinates": [
4.3123011,
52.0814892
]
},
"place": {
"type": "Point",
"coordinates": [
81320.4,
455347.397
]
},
"time": null
}
Goal
With this example file we want to demonstrate the use of temporal information in JSON-FG datasets. The JSON-FG draft specification enables to include temporal information in the time member of a file. The time member may contain an date object, time object or interval object, or either all three of them. However, there are requirements on including both a date and time object, thats is the date in the time object must be equal to the date in the date object.All times in JSON-FG
Process
We use again the full download of the BGT including history from PDOK.
The complete BGT file from PDOK is filtered for the topographical objects, but now we do not throw away the history.
The example datasets therefore describes both the historic situation and the current situation of of the BGT features. All geometry types in the file, expressed in WGS'84, are also valid GeoJSON geometries.
We create an example datasets with the GDAL draft implementation:
- a dataset with tijdstipregistratie and eindregistratie in the interval object of the time member.
Result
{
"type": "Feature",
"featureType": "vegetatieobject",
"coordRefSys": "[EPSG:28992]",
"properties": {
"lokaalid": "G0518.1e0a6f1604dee183e053530a0b0a8a7d",
"objectbegintijd": "2015-08-17",
"objecteindtijd": "2019-06-26",
"tijdstipregistratie": "2015-08-17T14:24:05",
"eindregistratie": "2019-06-26T15:08:45",
"lv-publicatiedatum": "2015-09-15T10:25:33",
"bgt-type": "niet-bgt",
"plus-type": "boom"
},
"geometry": null,
"place": {
"type": "Point",
"coordinates": [
81541.038,
455189.515
]
},
"time": {
"interval": [
"2015-08-17T13:24:05Z",
"2019-06-26T14:08:45Z"
]
}
}
Goal
With this example file we again want to demonstrate the use of temporal information in JSON-FG datasets.
Process
We download the ‘wijken-buurten-gemeenten’ datasets from 2003 to 2023 from the CBS website, and put them in a PostGIS database. Next we combine all the files according tot he municipality reorganizations since 2003:
-
If a municipality appears in a file but not in the following year, the municipality has been dissolved.
-
If a municipality does not appear in a file, but does appear in the following year, then a new municipality has been established.
We update the geometry with the latest available geometry in the datasets.
Ultimately, we export to a GPKG-file with municipalities including the code, name, creation date and termination date for each municipality.
Result
We created two example datasets of Dutch municipalities from 2003 to 2021: one with GeoJSON-geometries in the geojson member, and one without.
- Dutch municipalities 2003-2023 with geometry members
- Dutch municipalities 2003-2023 without geometry members
{
"type": "FeatureCollection",
"conformsTo": [
"[ogc-json-fg-1-0.1:core]"
],
"featureType": "Nederlandse gemeenten vanaf 2003",
"coordRefSys": "[EPSG:28992]",
"features": [
{
"type": "Feature",
"properties": {
"code": "0258",
"naam": "Kesteren",
"begingeldigheid": "2003-01-01",
"eindgeldheid": "2003-04-01"
},
"geometry": {
"type": "Polygon",
"coordinates": [
[
[
5.6053545,
51.9428509
],
...
[
5.6053545,
51.9428509
]
]
]
},
"place": {
"type": "Polygon",
"coordinates": [
[
[
170000.0,
439400.0
],
...
[
170000.0,
439400.0
]
]
]
},
"time": {
"interval": [
"2003-01-01",
"2003-04-01"
]
}
}
Goal
With this example file we want to demonstrate the use of 3D prisms in JSON-FG. The JSON-FG draft specification describes an easy way to include extruded point, line or polygon geometries.
Process
We use the LOD12_2d 3D BAG features as a source file. We import this layer in an PostGIS-database and create a SQL-script that writes the GeoJSON-representation of to the “base” property, the groundlevel to the “lower” property, and 70p-height to the “upper” property of the Prism.
Result
To be extended…
{
"type": "FeatureCollection",
"title": "SINGLE PRISM OBJECT FROM 3DBAG SURROUNDING BINNENHOF",
"conformsTo": [
"[ogc-json-fg-1-0.1:core]"
],
"features": [
{
"type": "Feature",
"properties": {
"identificatie": "NL.IMBAG.Pand.0518100000203254"
},
"geometry": {
"type": "Point",
"coordinates": [
4.310054697,
52.077976081
]
},
"place": {
"type": "Prism",
"base": {
"type": "Polygon",
"crs": {
"type": "name",
"properties": {
"name": "EPSG:7415"
}
},
"coordinates": [
[
[
81147.6875,
454955.46875
],
[
81155.7578125,
454946.59375
],
[
81162.0546875,
454951.375
],
[
81161.6171875,
454951.90625
],
[
81169.9453125,
454956.875
],
[
81168.2265625,
454960.5625
],
[
81165.03125,
454967.5625
],
[
81159.4609375,
454964.59375
],
[
81156.78125,
454962.5625
],
[
81147.6875,
454955.46875
]
]
]
},
"lower": 1.2849999666214,
"upper": 11.3428896665573
},
"time": {
"date": "1934-01-01"
}
}
]
}
File to be validated…
Goal With this example file we want to demonstrate the use of circular arc interpolation in JSON-FG. Currently, circular arc interpolation in JSON-FG is still under discussion and not part of the draft specification and . However, an propsal for it is made in this document: https://github.com/opengeospatial/ogc-feat-geo-json/blob/main/proposals/circular-geometry-objects.adoc
The BGT standard allows the application of circular arcs on top of the Simple Features. The use of circular arcs in the BGT is also a recurring discussion here: circular arcs would hinder the step to 3D and cause problems in maintaining the topology. However, the circular arcs are still included in the model and registration of the BGT for good reasons, namely the reduction of the number of coordinates and in line with the terrestrial method of collection.
For updating or exchanging the BGT source data based on JSON-FG, it is therefore recommended to extend the draft specification with circular string interpolation.
Process
The BGT test dataset contains features having CurvePolygon or CompoundCurves geometries. However, the GDAL implementation of JSON-FG interpolates circular arc strings to linestring segments, so we cannot use GDAL on our BGT dataset to get an example feature of an CurvePolygon in JSON-FG.
As the proposal for circular arcs looks pretty much like JSONify of the WKT of geometries, we alter the WKT geometry of the BGT to an JSON-FG-ish geometry in the place member.
Result
To be extended…
{
"type": "Feature",
"featureType": "wegdeel",
"coordRefSys": "[EPSG:28992]",
"properties": {
"lokaalid": "G0518.1e0a6f175bbae183e053530a0b0a8a7d",
"objectbegintijd": "2015-08-17T00:00:00Z",
"objecteindtijd": null,
"tijdstipregistratie": "2018-06-21T14:23:20Z",
"eindregistratie": "2021-11-22T16:40:21Z",
"lv-publicatiedatum": "2018-06-21T16:17:38Z",
"bgt-fysiekvoorkomen": "open verharding",
"plus_fysiekvoorkomen": "gebakken klinkers",
"bgt-functie": "voetpad",
"plus-functie": null
},
"geometry": null,
"place": {
{
"type": "CurvePolygon",
"coordinates": [
{
"type": "CompoundCurve",
"coordinates": [
{
"type": "Arc",
"coordinates": [
[
81181.685,
455198.326
],
[
81180.715,
455196.105
],
[
81181.004,
455189.334
]
]
},
{
"type": "LineString",
"coordinates": [
[
81181.004,
455189.334
],
[
81186.059,
455181.659
],
[
81186.651,
455180.761
],
[
81191.142,
455173.585
],
[
81197.21,
455162.659
],
[
81199.115,
455158.495
],
[
81203.405,
455160.479
],
[
81195.976,
455176.612
],
[
81194.726,
455178.463
],
[
81194.436,
455179.056
],
[
81194.067,
455179.194
],
[
81194.132,
455179.411
],
[
81181.685,
455198.326
]
]
}
]
}
}
}