I have a column with gps coordinates, in each row a set of geo-polygon coordinates. Most lines have duplicate gps coordinates (complete coincidence of longitude and latitude in one column).
Example:
MULTIPOLYGON
23.453411011874813 41.74245395132344
23.453972640029299 41.74214208390741
23.453977029220994 41.741827739090233
23.454523642352295 41.741515869012523
23.441100249526403 41.741203996333724
23.441661846243466 41.740892121053918
23.456223434003668 41.74058024317317
23.441661846243466 41.740892121053918
I need to remove duplicate coordinates (bold)
I'm using teradata 16.20.32.17
Thank you!
Have a look at SimplifyPreserveTopology, it's not exactly removing duplicates, but probably close to what you want:
Simplifies a geometry by removing points that would fall within a
specified distance tolerance.
The simplification always returns a
valid geometry. Simplified geometries require less storage space and
fewer spatial operations during geospatial manipulations. Consequently
operations on simplified geometries generally perform faster. Smaller
tolerance values result in a geometry closer to the input geometry,
but will remove fewer vertices. Larger tolerance values will remove
more vertices, but the resulting simplified geometry will be less
similar to the original input.
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 have an oracle database (11g spatial) that includes a series of area polygons and water mains. I'm trying to attribute each of these mains to the area in which it is contained and for the most part this is straightforward enough (using the SDO_CONTAINS function) but I'm not sure how to deal with mains that straddle multiple polygons due to errors in digitisation.
In cases like this what I'd ideally like to do is attribute a main to an area polygon if the majority of it's length (>50%) is contained within onit. I know that I can use the SDO_RELATE function to determine every polygon that any given main interacts with, but I don't know how to then go about determining how much of it's length is contained within each area.
The principle is like this:
Correlate mains and areas. Assuming you have many mains and many areas, the most efficient approach is to use SDO_JOIN
For each couple (main/area) returned, compute their intersection (SDO_GEM.SDO_INTERSECTION) and measure the length of that intersection (SDO_GEOM.SDO_LENGTH).
From those results, retain the area for each main where the length is the maximum
If you want a full SQL example, allow me a bit of time to write that using sample data.
So I added geometry columns to a spatial table and using some of the msdn references I ended up specifying the SRID as 0 like so:
update dbo.[geopoint] set GeomPoint = geometry::Point([Longitude], [Latitude], 0)
However, I believe this was a mistake, but before having to update the column, is 0 actually the default = 4326? The query works as long as I specify the SRID as 0 on the query, but I'm getting weird results in comparison to the geography field I have... SRID 0 does not exist in sys.spatial_reference_systems and I haven't been able to dig up any information on it. Any help would be appreciated.
A SRID of 0 doesn't technically exist, it just means no SRID -- ie, the default if you forget to set it. So, technically, you can still perform distance, intersection and all other queries, so long as both sets of geometries have a SRID of 0. If you have one field of geometries with a SRID of 0 and another set with a SRID that actually exists, you will most likely get very strange results. I remember scratching my head once when not getting any results from a spatial query in exactly this situation and SQL Server did not complain, just 0 results (for what is is worth Postgis will actually fail, with a warning about non-matching SRIDs).
In my opinion, you should always explicitly set the SRID of your geometries (or geographies, which naturally will always be 4326), as not only does it prevent strange query results, but it means you can convert from one coordinate system to another. Being able to convert on the fly from lat/lon (4326), to Spherical Mercator (3857), as used in Google Maps/Bing, which is in meters, or some local coordinate system, such as 27700, British National Grid, also in meters, can be very useful. SQL Server does not to my knowledge support conversion from one SRID to another, but as spatial types are essentially CLR types, there are .NET libraries available should you ever need to do so, see Transform/ Project a geometry from one SRID to another for an example.
If you do decide to change you geometries, you can do something like:
UPDATE your_table SET newGeom = geometry::STGeomFromWKB(oldGeom.STAsBinary(), SRID);
which will create a new column or to do it in place:
UPDATE geom SET geom.STSrid=4326;
where 4326 is just an example SRID.
There is a good reference for SRIDs at http://spatialreference.org/, though this is essentially the same information as you find in sys.spatial_reference_systems.
SRIDs are a way to take into account that the distances that you're measuring on aren't on a flat, infinite plane but rather an oblong spheroid. They make sense for the geography data type, but not for geometry. So, if you're doing geographic calculations (as your statement of "in comparison to the geography field I have"), create geography points instead of geometry points. In order to do calculations on any geospatial data (like "find the distance from this point to this other point"), the SRID of all the objects involved need to be the same.
TL;DR: Is the point on the Cartesian plane? Use geometry. Is the point on the globe? Use geography.
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.
I am using postgis for my spatial database.
in my database I have a set of lines in one table and a set of points in another table. How Is it possible to determine which fits best as a point of intersection of two lines? What i am after is something related to the st_intersection function.
PostGIS's ST_INTERSECTION will give you the geometry of the point of intersection between the two lines, and then a MIN(ST_DISTANCE([...], [...]) between this intersection and your points will give you the best fit.
http://www.postgis.org/docs/ST_Intersection.html
http://www.postgis.org/docs/ST_Distance.html