UI Sandbox - GED4GEM add simple geom views for low res visualization

[Ben Wyss]

[et=8h]
[at=15.5h]

The admin 0 polygon layer that is used is very detailed, and is slow to render in the UI.
Because of this we should add another admin 0 level polygon that is much more simplified.
This simplified geometry should be added to a view that is conglomerated with the attributes of the country info data and should be visible in the UI at large scale zoom.
The original geometry should then be used at a smaller scale zoom.

[Ben Wyss (bmwyss)]

attached is a shapefile of admin 0 that was used in GEM1

[Ben Wyss (bmwyss)]

The shapefile that we used for GEM1 is not compatible with the world admin 0 file that GED4GEM is using.
Because of this we can do a spatial join between the GED file and the GEM1 file to join the needed country code information to the GEM 1 file. Or we could take the GED file and simplify it.

[Ben Wyss (bmwyss)]

Before anything this table needs to be backed up before simplifying

[Ben Wyss (bmwyss)]

I used the simplify PostGIS function to create a new 'moresimplegeom' column. This could only be done after I made a backup of the original file, and removed the complex geom column.

[Ben Wyss (bmwyss)]

Something to consider when dropping a very large column:

Notes (http://original.jamesthornton.com/postgres/7.3/postgres/sql-altertable.html)

The DROP COLUMN command does not physically remove the column, but simply makes it invisible to SQL operations. Subsequent inserts and updates of the table will store a NULL for the column. Thus, dropping a column is quick but it will not immediately reduce the on-disk size of your table, as the space occupied by the dropped column is not reclaimed. The space will be reclaimed over time as existing rows are updated. To reclaim the space at once, do a dummy UPDATE of all rows and then vacuum, as in:

UPDATE table SET col = col;
VACUUM FULL table;

If a table has any descendant tables, it is not permitted to ADD or RENAME a column in the parent table without doing the same to the descendants --- that is, ALTER TABLE ONLY will be rejected. This ensures that the descendants always have columns matching the parent.

A recursive DROP COLUMN operation will remove a descendant table's column only if the descendant does not inherit that column from any other parents and never had an independent definition of the column. A nonrecursive DROP COLUMN (i.e., ALTER TABLE ONLY ... DROP COLUMN) never removes any descendant columns, but instead marks them as independently defined rather than inherited.

Changing any part of the schema of a system catalog is not permitted.

Refer to CREATE TABLE for a further description of valid arguments. The PostgreSQL User's Guide has further information on inheritance.

[Ben Wyss (bmwyss)]

to simplify the polygon I am using:
UPDATE eqged.gadm_country_facts set moresimplegeom = simplify(simplegeom,0.01);

[Ben Wyss (bmwyss)]

If there is a further need to generalize geometries this tutorial on Using the GeoTools feature-pregeneralized module might be helpful: http://docs.geoserver.org/stable/en/user/tutorials/feature-pregeneralized/feature-pregeneralized_tutorial.html