Questions about geospatial tutorial

Support
1

Dear Stardog support,

I just started to use Stardog to eventually set up a knowledge graph with some geospatial features.

For the very first steps I followed your "Stardog geospatial" tutorial ( Stardog Geospatial | Stardog Documentation Latest ) and downloaded your example data ( stardog-tutorials/stardog-geospatial/dclandmarks.ttl at master · stardog-union/stardog-tutorials · GitHub ). Then I switched to Studio, created a new database (with the "spatial.enabled" flag enabled!) and imported the example data to the default graph. After that the database has 65 edges. I also added the additional namespaces that are used in that data file.

Then I opened a new workspace tab with this query:

SELECT * WHERE {
?s ?p ?o .
}
LIMIT 1000

This shows 65 results.

The example query from the tutorial

prefix geo: http://www.opengis.net/ont/geosparql#
prefix geof: http://www.opengis.net/def/function/geosparql/
prefix : http://blog.stardog.com/geons/

SELECT ?geom ?feature {
?f a :Location ;
rdfs:label ?feature ;
geo:hasGeometry ?geom .
?geom geof:within ("POINT(-77.111 38.855)"^^geo:wktLiteral "POINT(-77.052 38.885)"^^geo:wktLiteral) .
}

shows 2 results. That all looks fine.

When I click an entry in the 65 results table from the first query and choose "Visualize" it switches to Explorer and I see one triple (in this case: "Location" - "type" - "Washington Monument"). Now I don't understand several things:

  • I thought that when I double click on "Location" that the other landmarks will also appear!?
  • In general: Double clicking on "Location" or "Washington Monument" does not show anything. I expected the see the "geo:*" links...
  • When I perform an "empty search" (with "All v" on the left of the input field) I get "No results". This happens in both "List" and "Graph" view.
  • According to the documentation ( Stardog Explorer | Stardog Documentation Latest ) Explorer should display the Location instances on a map. But in my case no map is displayed.

Am I doing something wrong?

Thanks a lot for your help!

P.S.: I just saw: GeoSparql queries not working - #3 by NielsHoffmann
Do I also have a licence problem?

2

Hi Markus,

Everything looks as expected, but you’re missing a model, which is required for Explorer to navigate your data.

I’ve attached a model that should work for you. Download the geoModel.trig file.

In Studio, go to:
Database → Admin → Load Data, then browse to the file.

The Load Data dialog will populate the remaining fields automatically (because it is a .trig file), so there’s no need to change them.

Then in Explorer, run the query

image
image1512×142 8.45 KB

This will find the all Location that have Geometry. You can then click the map icon to view the locations on a map.

Thanks

Joe

geoModel.trig (1.5 KB)

3

Hi Joe,

great, that works!

Thanks a lot,
Markus

1 Like
4

Hi Joe,

one additional question: I managed to visualize locations from your dataset, but no areas (nor my own "street" = WKT-linestring). Is it possible to also draw these elements in the Explorer map?

Thanks!

5

Markus,

Explorer’s map view is really geared towards showing locations as points on the map. It doesn’t currently render geometries like areas (polygons/envelopes) or lines (e.g. LINESTRING) as shapes on the map.

That said, with some creativity you could use points to represent your objects

  • represent an area using a few key points (e.g. corners or centroid)

  • sample points along a line to give a visual sense of it

Thanks

Joe

6

image
image1920×1105 865 KB

Here for example flight paths are represented as positions at 1 min intervals, with point diameter proportional to 1/altitude. Larger points are lower altitude. You can see aircraft landing and taking off.

7

OK, I understand. No problem, and good to know. I will create a QGIS plugin to read and visualize these geometries on a map…