Dist between two lat/long's in USA

Question

Hello,
Can anyone please give me the function(Oracle or some other function) to find the distance between two points(Both of them are in lat/longs). Both the points are within the boundary of US.
Thanks,

Answer 1

Hi,
In Oracle 8.1.6, we have Beta support
for Coordinate Systems. There is
Beta users guide available under PRODUCTS/SPATIAL.
With this functionality, you can calculate
the distance between two points
very accuratly.
Here is an example. I will go into details
below. Hope this helps. Thanks.
Dan
======
SAMPLE SQL: (sorry about the formatting)
select
mdsys.sdo_geom.sdo_length (
mdsys.sdo_cs.transform (
mdsys.sdo_geometry (2002, 8307, null,
mdsys.sdo_elem_info_array (1,2,1),
mdsys.sdo_ordinate_array (
-73.983014309,
40.749544981,
a.geometry.sdo_point.x,
a.geometry.sdo_point.y)),
MDSYS.SDO_DIM_ARRAY(
MDSYS.SDO_DIM_ELEMENT(
'X', -180, 180, .00000005),
MDSYS.SDO_DIM_ELEMENT(
'Y', -90, 90, .00000005)),
41004),
.00000005) * 6.213712e-04 DISTANCE_IN_MILES
from test_abi a
where
mdsys.sdo_nn (
a.geometry,
mdsys.sdo_geometry (
1, 8307,
mdsys.sdo_point_type (-73.983014309,
40.749544981,
null),
null, null),
'SDO_NUM_RES = 1') = 'TRUE';
DESCRIPTION:
============
1) The above query is returning the
nearest point to
(-73.983014309, 40.749544981)
and also returning the distance in miles.
TEST_ABI.geometry is stored in
longitude/latitude with 8307
as the SRID.
Note, if you set the SRID in the
SDO_GEOMETRY object, you must also
set the SRID in USER_SDO_GEOM_METADATA.
To find out more info on SRID 8307,
you can execute the following:
select wktext
from mdsys.cs_srs
where srid = 8307;
SDO_NN is the operator used to find
the nearest neighbor.
For nearest neighbor queries, you
may want to try using RTREE indexes,
also Beta in 8.1.6.
To create an RTREE index, omit
SDO_LEVEL and SDO_NUMTILES from
the create index statement of your
spatial index.
We plan to fully profile RTREE indexes
in 8.1.7 and recommend them when
appropriate. Nearest neighbor is an
excellent candidate for an RTREE index.
2) In the SELECT clause, we are calling
two functions:
SDO_LENGTH
SDO_CS.TRANSFORM
The first argument passed into SDO_LENGTH
is the return value from
CS_TRANSFORM (which will be a
projected SDO_GEOMETRY object).
The second argument to SDO_LENGTH
is an SDO_TOLERANCE.
3) The first argument to CS_TRANSFORM
is an SDO_GEOMETRY constructor for a
line string, where the first point of
the linestring is
(-73.983014309, 40.749544981),
and the second point is the nearest
neighbor resulting from SDO_NN.
This goal here is to project the
linestring so we can get an accurate
result from SDO_LENGTH.
The second argument to CS_TRANSFORM
a dim_array.
The third argument to CS_TRANSFORM
is the target SRID. In this example,
SRID 41004 is used. This will be
fairly accurate for the continental US.
The geometry constructor for the
linestring will be projected to
SRID 41004.
If more accurate results are desired,
you should use an SRID that corresponds
to a specific state plane projection.
Query the WKTEXT column in MDSYS.CS_SRS
to pick appropriate SRID's for projection.
i.e. If I knew my nearest neighbor result
is going to be in Georgia, I might
use SRID 1001 instead of 41004.
4) In the result of the select list, I am
multiplying by 6.213712e-04,
the conversion factor from meters to
miles.
Hope this helps. Thanks.
Dan