New answers tagged spatialite
0
If you export to a geopackage then GeoServer can server that as a vector tile set. Or you could write your own version using Geotools.
2
Approach 1: update each line of your database table using ogrinfo and WHERE statement (individual line update)
My first approach differs from your expectation. I do not try to run a command within Spatialite but to call Spatialite from the command line and provide the infos as variables to customize the SQL query.
You can try the following. My comments in ...
2
The linked answer (well found!) says to load the regex module using the .load command on the sqlite3 command line. This also works on the spatialite command line:
spatialite> select 1 where 'a' regexp 'b';
Error: no such function: regexp
spatialite> .load /usr/lib/sqlite3/pcre.so
spatialite> select 1 where 'a' regexp 'b';
spatialite> select 1 ...
4
It can be done in two steps.
First, add a new geometry column to you table:
SELECT AddGeometryColumn('my_table', 'my_new_geom_column', 4326, 'POINT');
Remember to change in the previous query my dummy values with the those that fit for database schema. The 4326 value is the SRID of the new geometry column, and if you don't make reprojection it must match ...
1
A very simple approach: calculate the length of the boundary as well as the area of the polygon, than use this to get the boundary/area ratio. Long boundary divided by small area results in a high value: thus you could define a threshold above which your polygons tend to be more or less like a line.
You could directly use Select by expression with an ...
2
How about using a QGIS function to create an "Oriented minimum bounding box"? The process creates a field called height and another width for each feature. You could then calculate the ratio of the two fields and set a threshold to what you consider elongated or not.
6
Spatialite 5.0 has a function "Circularity" http://www.gaia-gis.it/gaia-sins/spatialite-sql-latest.html.
computes the Circularity Index from the given Geometry by applying the
following formula:
index = ( 4 * PI * Sum(area) ) / ( Sum(perimeter) * Sum(perimeter) )
it only applies to Polygons or MultiPolygons with the following
interpretation:
...
4
You can use a compactness measure to determine the "circularity" of a polygon. See this question.
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You could use ST_MaximumInscribedCircle to find polygons which are "narrower" than a given distance. This will also find small polygons which are not elongated, so to filter those out you could use ST_Perimeter.
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