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Bill Bell edited comment on SOLR2125 at 9/21/10 6:44 PM:

OK so that makes sense. Youa re using distance at 45 degrees. So the eastwest would not extend
far enough.
Using http://en.wikipedia.org/wiki/Pythagorean_theorem would help on the eastwest 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 westeast 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 eastwest would not
extend far enough.
Using http://en.wikipedia.org/wiki/Pythagorean_theorem would help on the eastwest 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 westeast 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: SOLR2125
> URL: https://issues.apache.org/jira/browse/SOLR2125
> 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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