I have two circle on a map with Longitude, Latitude (point()) and Radius and now I would know if there is a SQL function that return true if those circle intersect ?
Thx for help.
Try:
If(ST_Distance(POINT(Long1, Lat1),POINT(Long2, Lat2))<=Radius1+Radius2, "INTERSECT","NO INTERSECTION")
Which is basically asking if the distance between the centers of the circles is <= the sum of their radii. If it is - they intersect.
Try ST_***() functions available in MySQL 5.6.
More information.
https://dev.mysql.com/doc/refman/5.6/en/spatial-relation-functions-object-shapes.html
https://www.percona.com/blog/2013/10/21/using-the-new-mysql-spatial-functions-5-6-for-geo-enabled-applications/
You indeed need to use the ST_*() functions and spatial operator functions, but Zamrony's answer is rather vague. So, what you need to do is to convert your circles into geometry data types and then you can use st_intersect() to see if the 2 circles intersect:
Use ST_Buffer() function to convert point and radius into geometry data type:
Returns a geometry that represents all points whose distance from the
geometry value g is less than or equal to a distance of d, or NULL if
any argument is NULL.
Pls read the description of ST_Buffer_Strategy() as well on how points making up the circle geometries are determined.
Use ST_Intersects() function to determine if the two geometries intersect each other.
Related
MYSQL ver 5.7
Requirement:
I have a bunch of POINT geometries in MYSQL table and I have to find all the POINT geometries that are within 5km distance/radius of a GEOMETRYCOLLECTION object.
GEOMETRYCOLLECTION may contain more than one type of geometries like POINT, POLYGON etc.
Sample GEOMETRYCOLLECTION data:
SET #g1 = ST_GeomFromText('GEOMETRYCOLLECTION(POINT (-156.366489591715 66.913750389327),POLYGON ((-156.357608905242 66.906958164897, -156.360302383363 66.9066027336476, -156.361997104194 66.9067073607308, -156.363616093774 66.9066368440642, -156.365477697938 66.9065867326059, -156.368127298976 66.9065970034393, -156.370061891681 66.9066888794808, -156.37182258022 66.9068547305222, -156.373286981259 66.9070724523969, -156.374390675008 66.9072952721882, -156.376359777088 66.9077681138541, -156.377706173961 66.9080113180204, -156.379222192708 66.9081328753119, -156.380729601039 66.9081591586452, -156.382562289578 66.9081211961453, -156.387571662487 66.9099676951007, -156.389320598943 66.9125180930134, -156.389291120818 66.9145787836353, -156.384722634367 66.9167899596735, -156.37955035 66.9195246586276, -156.372520662511 66.9209119638337, -156.360432280238 66.9215118034161, -156.355776993787 66.9203754471679, -156.34906598338 66.9180659711298, -156.347941981299 66.9174007836309, -156.346853913592 66.9167568252985, -156.34605399901 66.9158971169665, -156.346982815675 66.9151925950926, -156.346794497967 66.9144321773854, -156.345642955261 66.9140107294695, -156.343831364638 66.9136152003034, -156.342996512556 66.9130307378043, -156.343113243806 66.9123137492637, -156.343498096931 66.9119029992644, -156.344661664637 66.9111819440571, -156.345080786511 66.9105884961414, -156.345524286511 66.9099605023924, -156.347168040675 66.9098486503092, -156.348952756297 66.9096090419763, -156.348689200048 66.9089614565606, -156.349495732338 66.908706844061, -156.350786711503 66.9082992794783, -156.352211271917 66.9083472388533, -156.353952768789 66.90829894302, -156.355389368787 66.9082072242701, -156.356512531285 66.9079768284371, -156.356677961493 66.9078075857291, -156.356422527119 66.907644261771, -156.355901372953 66.9072802273965, -156.357608905242 66.906958164897)))');
Sample POINT data:
SET #p1 = ST_GeomFromText('GEOMETRYCOLLECTION(POINT (-156.342840017 66.9320439348))');
I have tried ST_DISTANCE_SPHERE(#g1,#p1) spatial function (which returns the value in meters) but it seems it doesn't support geometry types other than POINT and MULTIPOINT.
Then I have used:
ST_DISTANCE(#g1,#p1)
'0.015301834064271899'
I am unable to understand the what is the UNIT of this returned value in MYSQL 5.7?
I have searched a lot on the internet and there is no proper documentation available regarding the same. In POSTGIS, this can be done but I am struggling to do this in MYSQL ver 5.7.
Any help is appreciated.
Thanks in advance!
ST_Distance returns "distance" in degrees here - i.e. the flat map view of the shortest distance between shapes. This value cannot be mapped to real distance, as real world distance of 1 degree along parallel is different from distance of 1 degree along meridian except near the equator.
Looks like MySQL cannot correctly compute distance here. You would be better served by systems with more geospatial support, like PostgreSQL + PostGIS, or Google BigQuery, etc. They give you correct answer, you just need to replace ST_GeomFromText with ST_GeogFromText to work with spherical geographies.
In my database I have polygons stored. Now I need to search all the polygons that are within a certain radius.
Even if the polygon is only a small part inside the region, then it should be included inside the results (so once there is a minimal match, there is a match).
What is the best way to do this? I have been thinking about creating another polygon and search everything that intersects this, but don't know if this is a valid method?
Yes, I think it is the best approach. You can create a polygon using ST_BUFFER and then you can use ST_INTERSECT to find if polygons will intersect your polygon.
May be you can also do it using ST_DISTANCE. It will calculate minimum distance of a point from polygon.
Select ST_DISTANCE(polygons,POINT(x, y)) as distance, polygon_id from your_polygon_table WHERE distance <= 10
I struggled with the same issue and came up with the following that works well.
select this.poly, other.poly
from table this, table other
where this.name = 'name of subject polygon'
and ST_Distance(ST_Centroid(this.polygon),ST_Centroid(other.polygon)) < 'desired distance';
This will work with the initial point is in the same table as the other polygons. If you have a fixed initial point you can simplify the query as follows:
select poly from table
where ST_Distance('26.36, -81.07',ST_Centroid(other.polygon)) < 'desired distance';
I am having trouble understanding ST_GeomFromText. It looks like there are 3 sets of 2 numbers. Why is that? Wouldn't coordinates just consist of a latitude and longitude?
Here is an example from http://postgis.net/docs/ST_GeomFromText.html:
SELECT ST_GeomFromText('LINESTRING(-71.160281 42.258729,-71.160837 42.259113,-71.161144 42.25932)');
ST_GeomFromText() takes a WKT expression of a geometry object and
Constructs a PostGIS ST_Geometry object from the OGC Well-Known text representation.
The WKT expression in the example is a LINESTRING which is
a one-dimensional object representing a sequence of points and the line segments connecting them.
You might think a linestring would be two-dimensional, but it's not, because a line has no width or height. (Points are 0-dimensional, polygons are 2-dimensional).
So, by definition, that would have more than one set of coordinates. A pair of coordinates would be a POINT, not a linestring, and would look something like this, in conjunction with the function in question:
ST_GeomFromText('POINT (30 10)');
You may want to read up on some GIS fundamentals:
http://www.cise.ufl.edu/~mschneid/Service/Tutorials/TutorialSDT.pdf - excellent tutorial
http://www.opengeospatial.org/standards/orm - OGC Reference Model
I have the following latitude and longitude:
lat - 18.9802767
lng - 72.8142511
I am trying the following query for places withint 10 kms from the point of interest.
select mbrcontains( geomfromtext(
'LINESTRING(72.8993663648088 19.0702857,72.72913583519122 18.8902677)'
),
geomfromtext(
'point(18.9802767 72.8142511)'
) );
The Linestring geometry object is derived from the exact point that I am trying to determine is within using the method for mysql 5.1 and above from this example using the formula :
linestring(point(#lng+10/(111.1/cos(radians(#lat))),#lat+10/111.1), point(#lng-10/(111.1/cos(radians(#lat))),#lat-10/111.1))
From what I understand the point falls within the Minimum Bounding Rectangle (MBR). However the query returns a 0 for the answer. The above is following the principles given in this example.
What is wrong with the query? How can I know if the point is within a certain geospatial distance (in this case the MBR points are calculated using 10 kms from the point given by co-ordinates: lat - 18.9802767, lng - 72.8142511).
BTW, I am using MySQL 5.5.32.
Your point does not fall within the MBR of the line. Looks like you've reversed the latitude or longitude coordinates on either the line or the point. Switch the X and Y in 'point(18.9802767 72.8142511)' to get this point, which will be within the MBR of the line:
POINT (72.8142511 18.9802767)
If you are tied to MySQL, you may consider updating to MySQL 5.6, then using the Buffer function to create a circular area from your point of interest, and then use ST_Within to find anything within that circular area.
If you are not tied to MySQL, consider PostGIS, which provides a nice ST_DWithin function that makes these comparisons very easy.
My question is somewhat related to this similar one, which links to a pretty complex solution - but what I want to understand is the result of this:
Using a Mysql Geometry field to store a small polygon I duly ran
select AREA(myPolygon) where id =1
over it, and got an value like 2.345. So can anyone tell me, just what does that number represent seeing as the stored values were long/lat sets describing the polygon?
FYI, the areas I am working on are relatively small (car parks and the like) and the area does not have to be exact - I will not be concerned about the curvature of the earth.
2.345 of what? Thanks, this is bugging me.
The short answer is that the units for your area calculation are basically meaningless ([deg lat diff] * [deg lon diff]). Even though the curvature of the earth wouldn't come into play for the area calculation (since your areas are "small"), it does come into play for the calculation of distance between the lat/lon polygon coordinates.
Since a degree of longitude is different based on the distance from the equator (http://en.wikipedia.org/wiki/Longitude#Degree_length), there really is no direct conversion of your area into m^2 or km^2. It is dependent on the distance north/south of the equator.
If you always have rectangular polygons, you could just store the opposite corner coordinates and calculate area using something like this: PHP Library: Calculate a bounding box for a given lat/lng location
The most "correct" thing to do would be to store your polygons using X-Y (meters) coordinates (perhaps UTM using the WGS-84 ellipsoid), which can be calculated from lat/lon using various libraries like the following for Java: Java, convert lat/lon to UTM. You could then continue to use the MySQL AREA() function.