[GIS] Loading Postgis Layers in a desktop application using C#

cpostgis

I have layers in a postgis database that I can load in a MapWindows Control (ocx) using a npgsql connection and creating a shapefile using the geometry field in a Visual Studio .Net 2010 (C#) application, but this is really slow when the layer contains too many features.

I have seen that QGIS loads postgis layers very fast and I want to know if is possible to use the QGIS functionality in any way in a Forms Application using C#, like a DLL or an ocx control. I need to load postgis layers in a display control with legend and be able to change colors, symbology, labels, etc. Also, I need to save any changes in the layer to the postgis database.

Any help will be appreciated.

Thanks.

Update:

Unicoletti, thanks for your reply.

I don't see the way to use swig to open a postgis layer and show it in a windows forms. I was wondering if there is any way to encapsullate qgis functionality to do that.

I want to have a control in a form and programatically open a postgis layer on it and, later, manage the properties of that layer, line color, fill color, legends,… Right now I'm using MapWindows ocx but loading postgis layers is really slow, as it's made creating a shapefile and adding shapes to it one by one (using feature data objects).

If you know where to find a complete application example that loads a postgis layer using QGis functionality in c# or even in c++, it would be very appreciated.

Thanks, and sorry for my bad english.

Best Answer

Have you tried SharpMap (http://sharpmap.codeplex.com/) or DotSpatial (http://dotspatial.codeplex.com/)? Both are native CLR libraries that can access and render PostGIS data (among others).

Bill

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[GIS] Alternatives to ogr2ogr for loading large GeoJson file(s) to PostGIS

Unfortunately JSON is, much like XML, badly suited for stream processing so almost all implementations require that the whole dataset be loaded in memory. While this is ok for small sets in your case there is no other option than breaking the dataset into smaller, manageable chunks.

Improving on Pablo's solution, here's one that does not require you to actually open and load the file into an editor and split by hand but tries to automate as much as possible the whole process.

Copy the json file onto a Unix host (linux, osx) or install cygwin tools on Windows. Then open a shell and use vim to remove first and last row from the file:

$ vim places.json

type dd to remove the first line, then SHIFT-G to move the end of the file, type dd again to remove last line. Now type :wq to save the changes. This should take just a couple of minutes at most.

Now we will harness the sheer power of unix to split the file in more manageable chunks. In the shell type:

$ split -l 10000 places.json places-chunks-

Go grab a beer. This will split the file into many smaller files, each containing 10000 lines. You can increase the number of lines, as long as you keep it small enough so that ogr2gr can manage it.

Now we are going to stick head and tail to each of the files:

$ echo '{"type":"FeatureCollection","features":[' > head
$ echo ']}' > tail
$ for f in places-chunks-* ; do cat head $f tail > $f.json && rm -f $f ; done

Go grab a snak. The first two commands simply create a header and footer file with the correct contents (just for convenience really), while the last will add header and footer to each of the chunks that we split above and remove the headerless/footerless chunk (to save space).

At this point you can hopefullyprocess the many places-chunks-*.json files with ogr2ogr:

$ for f in places-chunks-*.json ; do ogr2ogr -your-options-here $f ; done

[GIS] Create Spatial Index in PostGIS on an entire Schema

If you want to batch create indexes on geometry columns, you could try this plpgsql function I've just knocked up:

CREATE OR REPLACE FUNCTION BatchIndex(sn text, tn text, cn text) RETURNS void AS $$
DECLARE i_exists integer;
DECLARE idxname text;
BEGIN
  idxname := 'idx_' || tn || '_' || cn;
  select into i_exists count(*) from pg_class where relname = idxname;

  IF i_exists = 0 THEN
    EXECUTE 'CREATE INDEX ' ||idxname || ' ON '
      || sn || '.' || tn
      || ' USING GIST(' || cn || ')';
  END IF;
END;
$$ LANGUAGE plpgsql;

I've not tried it in anger on my database, but it seems to do the job.

To use it, just run a SELECT statement like this:

select BatchIndex('public', f_table_name, f_geometry_column) from geometry_columns where f_table_schema = 'public';

To create indexes on all geometry columns, you can use it like this:

select BatchIndex(f_table_schema, f_table_name, f_geometry_column) from geometry_columns;

Afterwards, run a VACUUM ANALYZE to tidy everything up.

Best Answer

Related Solutions

[GIS] Alternatives to ogr2ogr for loading large GeoJson file(s) to PostGIS

[GIS] Create Spatial Index in PostGIS on an entire Schema

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