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https://issues.apache.org/jira/browse/JENA-1915?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andy Seaborne reassigned JENA-1915:
-----------------------------------
Assignee: Greg Albiston
> spatial:greatCircle appears to be returning wrong answers
> ---------------------------------------------------------
>
> Key: JENA-1915
> URL: https://issues.apache.org/jira/browse/JENA-1915
> Project: Apache Jena
> Issue Type: Bug
> Components: Spatial
> Affects Versions: Jena 3.13.1
> Reporter: Bryon Jacob
> Assignee: Greg Albiston
> Priority: Major
> Time Spent: 20m
> Remaining Estimate: 0h
>
> the `spatial:greatCircle` function appears broken - sometimes returning
> negative numbers. returning negative numbers can never be correct from a
> distance function - but I've tried to produce something more useful than that
> as a defect report and repro...
> I was trying to "port" some SPARQL queries where I'd written the great circle
> function (Haversine formula) to use the spatial:greatCircle function - which
> means I had a pretty good test case to see where the issue arises. I
> simplified my query down to a repeatable test that demonstrates the issue:
> note that in my original query, I was using a custom jena function to compute
> `radians` - since that function won't be available to you in stock jena to
> try this out, I've precomputed the radians values and put them in the VALUES
> block next to lat/lon pairs. This should be runnable on any stock Jena
> instance with the jena-geosparql functions loaded. Note that for most of the
> distances computed, the two distances agree quite closely - but for the last
> two, the jena function returns a negative number, where the hand-computed
> value is a correct distance between those points
> {code:java}
> PREFIX m: <http://www.w3.org/2005/xpath-functions/math#>
> PREFIX spatial: <http://jena.apache.org/function/spatial#>
> # this is a namespace of custom functions, which won't be available in stock
> Jena - to reproduce
> # this, I've pre-computed the radian values and included them in a VALUES
> block below...
> # PREFIX f: <http://data.world/function/functions#>
> SELECT ?lat1 ?lon1 ?lat2 ?lon2 ?φ1 ?φ2 ?Δφ ?Δλ ?d1 ?d2
> WHERE {
> VALUES (?lat1 ?lon1 ?lat2 ?lon2 ?φ1 ?φ2 ?Δφ ?Δλ) {
> # in my original query, I was computing radians using a custom
> radians function, which won't be available
> # in stock Jena, so to make this reproducible I precomputed the
> radians values needed for the Haversine
> (41.2572 -95.9656 41.2592 -95.9339 0.7201 0.7201
> 0.0000 0.0006)
> (41.2572 -95.9656 41.2482 -96.072 0.7201 0.7199
> -0.0002 -0.0019)
> (41.2572 -95.9656 41.5871 -93.626 0.7201 0.7258
> 0.0058 0.0408)
> (41.2572 -95.9656 51.0472 -113.9998 0.7201 0.8909
> 0.1709 -0.3148)
> (41.2572 -95.9656 40.7528 -73.9876 0.7201 0.7113
> -0.0088 0.3836)
> (41.2572 -95.9656 49.7237 13.3422 0.7201 0.8678
> 0.1478 1.9078)
> (41.2572 -95.9656 -33.9065 18.4175 0.7201
> -0.5918 -1.3119 1.9964)
> (41.2572 -95.9656 -33.8646 151.2099 0.7201
> -0.5910 -1.3111 4.3140)
> }
>
> # calculate the "great circle" distance between the two (lat φ, long λ)
> points, in kilometers.
> # these are the function calls in my original query, commented out and
> replaced with VALUES above
> # BIND (f:radians(?lat1) AS ?φ1)
> # BIND (f:radians(?lat2) AS ?φ2)
> # BIND (f:radians(?lat2 - ?lat1) AS ?Δφ)
> # BIND (f:radians(?lon2 - ?lon1) AS ?Δλ)
> BIND (m:sin(?Δφ / 2) * m:sin(?Δφ / 2) + m:cos(?φ1) * m:cos(?φ2) *
> m:sin(?Δλ / 2) * m:sin(?Δλ / 2) AS ?a)
> BIND (2 * m:atan2(m:sqrt(?a), m:sqrt(1 - ?a)) AS ?c)
> BIND (6371 AS ?RadiusOfEarthInKm)
> BIND (?RadiusOfEarthInKm * ?c AS ?d1)
> # call the Jena function for comparison
> BIND(spatial:greatCircle(?lat1, ?lon1, ?lat2, ?lon2,
> <http://www.opengis.net/def/uom/OGC/1.0/kilometre>) AS ?d2)
> }
> {code}
>
>
>
>
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