To create a polygon around a pair of lat+lon coordinates I'd expect to be able to buffer the geogpoint:
e.g. ST_BUFFER(ST_GEOGPOINT(lat, lon), 1000)
This creates a circular polygon with a radius of 1000m.
Bigquery doesn't seem to have the buffer function, which seems like a really basic one - am I missing something? Thanks!
As for now, ST_BUFFER function is not supported in query engine yet. All available geography functions in Standard SQL you can see here. Additionally, you can think about using buffer function from the open source library Turf.JS to make buffers and use it in BigQuery:
jslibs.turf.ST_BUFFER(geometry_to_buffer GEOGRAPHY, radius NUMERIC, units STRING, steps NUMERIC)
Please follow carto tutorial to learn more about using this function.
ST_Buffer is now available (in preview)
https://cloud.google.com/bigquery/docs/reference/standard-sql/geography_functions#st_buffer
There is also ST_BufferWithTolerance which allows one to specify approximation tolerance, rather than number of segments in polygon approximating the buffer.
Related
I'm looking at the freely available Solar potential dataset on Google BigQuery that may be found here: https://bigquery.cloud.google.com/table/bigquery-public-data:sunroof_solar.solar_potential_by_censustract?pli=1&tab=schema
Each record on the table has the following border definitions:
lat_max - maximum latitude for that region
lat_min - minimum latitude for that region
lng_max - maximum longitude for that region
lng_min - minimum longitude for that region
Now I have a coordinate (lat/lng pair) and I would like to query to see whether or not that coordinate is within the above range. How do I do that with BQ Standard SQL?
I've seen the Geo Functions here: https://cloud.google.com/bigquery/docs/reference/standard-sql/geography_functions
But I'm still not sure how to write this query.
Thanks!
Assuming the points are just latitude and longitude as numbers, why can't you just do a standard numerical comparison?
Note: The first link doesn't work without a google account, so I can't see the data.
But if you want to become spatial, I'd suggest you're going to need to take the border coordinates that you have and turn them into a polygon using one of: ST_MAKEPOLYGON, ST_GEOGFROMGEOJSON, or ST_GEOGFROMTEXT. Then create a point using the coords you wish to test ST_MAKEPOINT.
Now you have two geographies you can compare them both using ST_INTERSECTION or ST_DISJOINT depending on what outcome you want.
If you want to get fancy and see how far aware from the border you are (which I guess means more efficient?) you can use ST_DISTANCE.
Agree with Jonathan, just checking if each of the lat/lon value is within the bounds is simplest way to achieve it (unless there are any issues around antimeridian, but most likely you can just ignore them).
If you do want to use Geography objects for that, you can construct Geography objects for these rectangles, using
ST_MakePolygon(ST_MakeLine(
[ST_GeogPoint(lon_min, lat_min), ST_GeogPoint(lon_max, lat_min),
ST_GeogPoint(lon_max, lat_max), ST_GeogPoint(lon_min, lat_max),
ST_GeogPoint(lon_min, lat_min)]))
And then check if the point is within particular rectangle using
ST_Intersects(ST_GeogPoint(lon, lat), <polygon-above>)
But it will likely be slower and would not provide any benefit for this particular case.
I need to calculate distance of two positions on OrientDB with new Spatial Module which is available for version 2.2. I have checked documentation (http://orientdb.com/docs/2.2/Spatial-Module.html) but couldn't find anything. I can calculate distance on my own but that time, what is the point to use the Spatial Module if I will not use spatial capabilities?
Also I need to check that if two positions are less than a threshold value. Again I don't have any documentation given by OrientDB.
Here are the two Java method signatures that I'm trying to implement.
double distance(Vertex gateway, Vertex sink);
boolean isInDistance(Vertex from, Vertex to, double distanceX, double distanceY);
Actually out of already implemented SQL-MM functions, ST_DISTANCE is needed to be implemented. I need a solution as a ST_DISTANCE replacement, I guess.
Thank you for your help.
Is there a function or any round about way to translate/move a geometry to specific (x,y) in Oracle Spatial 11g, as that can be achieved by the ST_Translate function provided by PostGIS (Link: https://postgis.net/docs/ST_Translate.html)?
Regards,
Shiva Shankar
Yes, you can do that. Check out the SDO_UTIL.AFFINETRANSFORMS() function. It can perform multiple changes to a geometry: translation but also scaling, rotation, reflection and shearing.
You can combine several of those operations in a single call. The operations work in 2D or 3D.
I'm working with postgresql with postgis.
I have few questions:
trying to insert into a table with polygon column using the following syntax:
ST_GeomFromText('POLYGON((long1 lat1, long2 lat2, long3 lat3))')
fails with the following error: function geomfromtext(unknown) does not exist
what is the difference between
CREATE TABLE my_table (my_polys polygon);
and
CREATE TABLE my_table2 (my_polys GEOGRAPHY(POLYGON));
and why does the following:
INSERT INTO my_table (my_polys) VALUES ('
(51.504824, -0.125918),
(51.504930, -0.122743),
(51.504930, -0.110297),
(51.504824, -0.102229),
(51.503435, -0.099311)'
);
work fine with my_table and not with my_table2 (I've changed the table name to my_table2)
what is the maximum number of points a polygon can have?
The geography data type is mostly useful when your geometry might wrap around the date line. If it does not, you are better off using normal geometry data types, as most functions in Postgis are designed to work on planar geometries. If your data are lat/lon, you can explicitly set this when you create your column with:
create table foo geom geometry(POLYGON, 4326);
Explicitly setting the coordinate reference system is useful if you want to convert between one coordinate system and another and helps prevent suprises if you attempt to run an intersection, say, between geometries in different coordinate systems.
It is hard to imagine your insert fragment above working with any table, not only is there a trailing comma, but there is no st_geomfromtext, st_makepolygon or anything else to convert what you have written into any geometry.
I have no idea what the maximum size for a polygon is, although, as Chris has already said, you are likely to have performance issues with polygons of 1gb in size, when you try and do spatial queries on them.
Your polygon size is limited by the max storage size. I believe this is limited to 1gb for a toasted column, though my guess is that you are likely to run into performance issues long before you exceed the maximum number of points.
Polygon is a built in type in PostgreSQL, and PostGIS offers additional types for geometry and geography. As I understand it the built-in-types only work for 2d Euclidean space, while PostGIS offers additional options there.
As for why your query fails, I wonder which version of PostGIS you are running and why st_geomfromtext is calling geomfromtext.
We have an application that has a database full of polygons (currently stored as points) that a .net app pulls out and checks if they overlap.
I occurred to me that it would be much nicer to convert these point arrays to polygon / polyline objects within the database and use sql to get a bool of weather they overlap or not.
I have seen different methods suggested to do this but non of the examples given were quite in-line with my needs.
I would be very happy to receive input from those kind enough to offer their experience.
Additional:
In response to questions: It is indeed 2D. and yes any crossover of the two is considered true. The polygons have n points and can be concave. The polygons will be saved as 1 per row (after data conversion task) as polygons (i.e. the polygon type .. it might be called something else spatial / geom my memory is not on my side right now)
You can use .STIntersection with .STAsText() to test for overlapping polygons. (I really hate the terminology Microsoft has used (or whoever set the standard terms). "Touching," in my mind, should be a test for whether or not two geometry/geography shapes overlap at all, not just share a border.)
Anyway....
If #RadiusGeom is a geometry representing a radius from a point, the following will return a list of any two polygons where an intersection (a geometry that represents the area where two geometries overlap) is not empty.
SELECT CT.ID AS CTID, CT.[Geom] AS CensusTractGeom
FROM CensusTracts CT
WHERE CT.[Geom].STIntersection(#RadiusGeom).STAsText() <> 'GEOMETRYCOLLECTION EMPTY'
If your geometry field is spatially indexed, this runs pretty quickly. I ran this on 66,000 US CT records in about 3 seconds. There may be a better way, but since no one else had an answer, this was my attempt at an answer for you. Hope it helps!
Calculate and store the bounding rectangle of each polygon in a set of new fields within the row which is associated with that polygon. (I assume you have one; if not, create one.) When your dotnet app has a polygon and is looking for overlapping polygons, it can fetch from the database only those polygons whose bounding rectangles overlap, using a relatively simple SQL SELECT statement. Those polygons should be relatively few, so this will be efficient. Then, your dotnet app can perform the finer polygon overlap calculations in order to determine which ones of those really overlap.
Okay, I got another idea, so I am posting it as a different answer. I think my previous answer with the bounding polygons probably has some merit on its own, even if it was to reduce the number of polygons fetched from the database by a small percentage, but this one is probably better.
MSSQL supports integration with the CLR since version 2005. This means that you can define your own data type in an assembly, register the assembly with MSSQL, and from that moment on MSSQL will be accepting your user-defined data type as a valid type for a column, and it will be invoking your assembly to perform operations with your user-defined data type.
An example article for this technique on the CodeProject: Creating User-Defined Data Types in SQL Server 2005
I have never used this mechanism, so I do not know details about it, but I presume that you should be able to either define a new operation on your data type, or perhaps overload some existing operation like "less-than", so that you can check if one polygon intersects another. This is likely to speed things up a lot.