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https://issues.apache.org/jira/browse/SOLR-2125?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12913244#action_12913244
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Bill Bell edited comment on SOLR-2125 at 9/21/10 6:44 PM:
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OK so that makes sense. Youa re using distance at 45 degrees. So the east-west
would not extend far enough.
Using http://en.wikipedia.org/wiki/Pythagorean_theorem would help on the
east-west case, but circle or ellipses is MUCH better.
Although extending the 45 degree out would be a conservative estimate. And
since we usually sort by distance asc, those extra points would be in the
result set but at the end of the list. (this is an improvement - again not at
good as ellipses).
You need a quick function that tells you "is this lat,long in the circle /
ellipses or not". A range [X to Y] will not get you that. You need to use
hsin().
On potential:
1. Do range select using points
http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates
(Lat => 1.2393 AND Lat <= 1.5532) AND (Lon >= -1.8184 AND Lon <= 0.4221)
2. Check those points for distance "in the ellipses".
http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates
acos(sin(1.3963) * sin(Lat) + cos(1.3963) * cos(Lat) * cos(Lon - (-0.6981)))
<= 0.1570;
That should make it fast and simplify the calculations.
UPDATE - NOTE:
Plugging all this into the web site, proves that Pythagorean is a good
approximation...
See Excel attached.
hsin = 309 km from pt to max
hsin = 314 km from pt to min
Estimate using Pythagorean is 311 using sqrt(220km^2+220km^2)
41.42% is the difference from west-east to 45 degree. sqrt(1^2+1^2)
Yonik: sqrt(2) is right - but the spreadsheet is a bit better based on spheres.
The #2 will then subselect the points to limit within that result set.
Therefore, a user could take a distance from the user, sqrt(d^2+d^2) and use
that to get a list - it is not exact but better than nothing.
was (Author: billnbell):
OK so that makes sense. Youa re using distance at 45 degrees. So the
east-west would not extend far enough.
Using http://en.wikipedia.org/wiki/Pythagorean_theorem would help on the
east-west case, but circle or ellipses is MUCH better.
Although extending the 45 degree out would be a conservative estimate. And
since we usually sort by distance asc, those extra points would be in the
result set but at the end of the list. (this is an improvement - again not at
good as ellipses).
You need a quick function that tells you "is this lat,long in the circle /
ellipses or not". A range [X to Y] will not get you that. You need to use
hsin().
On potential:
1. Do range select using points
http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates
(Lat => 1.2393 AND Lat <= 1.5532) AND (Lon >= -1.8184 AND Lon <= 0.4221)
2. Check those points for distance "in the ellipses".
http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates
acos(sin(1.3963) * sin(Lat) + cos(1.3963) * cos(Lat) * cos(Lon - (-0.6981)))
<= 0.1570;
That should make it fast and simplify the calculations.
UPDATE - NOTE:
Plugging all this into the web site, proves that Pythagorean is a good
approximation...
See Excel attached.
hsin = 309 km from pt to max
hsin = 314 km from pt to min
Estimate using Pythagorean is 311 using sqrt(220km^2+220km^2)
41.42% is the difference from west-east to 45 degree. sqrt(1^2+1^2)
The #2 will then subselect the points to limit within that result set.
Therefore, a user could take a distance from the user, sqrt(d^2+d^2) and use
that to get a list - it is not exact but better than nothing.
> Spatial filter is not accurate
> ------------------------------
>
> Key: SOLR-2125
> URL: https://issues.apache.org/jira/browse/SOLR-2125
> Project: Solr
> Issue Type: Bug
> Components: Build
> Affects Versions: 1.5
> Reporter: Bill Bell
> Assignee: Grant Ingersoll
> Attachments: solrspatial.xlsx
>
>
> The calculations of distance appears to be off.
> Note: "The radius of the sphere to be used when calculating distances on a
> sphere (i.e. haversine). Default is the Earth's mean radius in kilometers
> (see org.apache.solr.search.function.distance.Constants.EARTH_MEAN_RADIUS_KM)
> which is set to 3,958.761458084784856. Most applications will not need to set
> this."
> The radius of the earth in KM is 6371.009 km (≈3958.761 mi).
> Also filtering distance appears to be off - example data:
> 45.17614,-93.87341 to 44.9369054,-91.3929348 Approx 137 miles Google. 169
> miles = 220 kilometers
> http://....../solr/select?fl=*,score&start=0&rows=10&q={!sfilt%20fl=store_lat_lon}&qt=standard&pt=44.9369054,-91.3929348&d=280&sort=dist(2,store,vector(44.9369054,-91.3929348))
> asc
> Nothing shows. d=285 shows results. This is off by a lot.
> Bill
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