Thursday, April 19, 2018

My Geo Web Application Development Tech Stack

I thought that it would be interesting to post a list of technologies that I use in my so called "technology stack".  The day to day work happens in Ubuntu, PyCharm, Visual Studio Code, Postgresql (PgAdmin 4) all from my new Dell XPS 15 9560 rockin with 16 GB Ram and 512 GB SSD. My old Dell Precision m4500 lasted 7 years until the harddrive failed.  It is still alive with a new 512 GB SSD and running Ubuntu, sorry Windows.



Tuesday, April 10, 2018

How to backup Postgresql DB to an FTP site using Python

Using the standard tools of Postgresql pg_dump and Python's subprocess module we can call the command line tool via Python and have the dump file uploaded to an FTP site.  This is of course a very simple way to backup.

An alternative would be to use Pgbarman https://www.pgbarman.org/ which is a higly effective way to minimize data loss.

Here you go:


Sunday, February 11, 2018

How to create a regular survey grid with PostGIS

A fishnet grid is also commonly called a: survey grid, raster sample, sample grid, grid, landscape grid, grid reference and of course fishnet.



It all depends on your field of expertise as to what you call it, I know some times in biology they use the term "landscape grid".

If you are the data analyst, gis analyst or even coop student who is assigned the job of creating such a sample grid as a set of polygons using Postgresql with PostGIS here is the function you could create in the database.

As you see in the GIST here there is also sample sql select query that would generate the data for you using the default start location of x= 0.0 and y=0.0.

The input parameters are as follows:

  1. number of rows of the grid
  2. number of columns of the grid
  3. start x coordinate (optional, default is 0.0)
  4. start y coordinate (optional, default is 0.0)
  5. row width in meters (if coordinates are a meter based system)
  6. column width in meters (if coordinates are in a meter based system)
You could run this query in in QGIS and visualize the result immediately and save as a Shapefile using the QGIS "save as" functionality.

have fun generating your fishnet :)

source: https://trac.osgeo.org/postgis/wiki/UsersWikiCreateFishnet

Michael

Tuesday, January 30, 2018

AGEO 2018 Presentation

I am invited to present indrz at the annual AGEO 2018 http://www.ageo.at Österreichischer Dachverband für Geographische Information (Austrian Umbrella Organization for Geographic Information).  Presentation 28.02.2018 is now available for download and viewing:   https://goo.gl/4mchWX



Wednesday, December 21, 2016

How to create Django translations for django-rosetta from a model field

How to create Django translations from a model field for django-rosetta?



I am using Django-Rosetta to handle all of my project translations.  Unfortunately I have only one model and one field of data that needs translation, the name of the POI.  To get around this I have created a little script to query my Django Database directly to deliver the list of names to be translated.  The output is a new html file with "trans" tags.  This html file is then placed in my templates folder so that "makemessages" can find the file and mark them for translation.

Anytime I want to update this I can run this script and bingo, new template file and new translations.

Note to self:  When adding msgid and msgstr  by hand the command "makemessages" will remove them in the .po file every time the command is called.


Tuesday, September 13, 2016

CORS with Geoserver 2.9.0 and Tomcat


How to enable CORS on your Geoserver 2.9.0 running on Tomcat.


This is taken directly from the tomcat homepage https://tomcat.apache.org/tomcat-7.0-doc/config/filter.html#CORS_Filter


add the following code to your  web.xml  file then stop/start the tomcat process

service tomcat stop
service tomcat start

<filter>
  <filter-name>CorsFilter</filter-name>
  <filter-class>org.apache.catalina.filters.CorsFilter</filter-class>
  <init-param>
    <param-name>cors.allowed.origins</param-name>
    <param-value>*</param-value>
  </init-param>
  <init-param>
    <param-name>cors.allowed.methods</param-name>
    <param-value>GET,POST,HEAD,OPTIONS,PUT</param-value>
  </init-param>
  <init-param>
    <param-name>cors.allowed.headers</param-name>
    <param-value>Content-Type,X-Requested-With,accept,Origin,Access-Control-Request-Method,Access-Control-Request-Headers</param-value>
  </init-param>
  <init-param>
    <param-name>cors.exposed.headers</param-name>
    <param-value>Access-Control-Allow-Origin,Access-Control-Allow-Credentials</param-value>
  </init-param>
  <init-param>
    <param-name>cors.support.credentials</param-name>
    <param-value>true</param-value>
  </init-param>
  <init-param>
    <param-name>cors.preflight.maxage</param-name>
    <param-value>10</param-value>
  </init-param>
</filter>
<filter-mapping>
  <filter-name>CorsFilter</filter-name>
  <url-pattern>/*</url-pattern>
</filter-mapping>

Thursday, September 1, 2016

Using Django to create a point GeoJSON feature from the centroid of a polygon

A practical example showing how to use geoDjango geospatial functions to create the centroid of a polygon, returning a GeoJSON dataset that includes all the attributes of the original polygon feature excluding the original  geometry.

Why exclude the original geometry you are probably asking yourself?  Simple, the response already will include each individual geometry representing the original so we do not want it to be duplicated in the resonse.

Libraries used:

  1. Django Rest Framework to server up the response but you could of course use simple the Django response as well.
  2. Python GeoJSON to create the features.  
How to use it:


You will need to hook up your Django URLs to actually use this new view function.  You will only need to pass in a unique_id value to return a single point centroid from your input polygon feature.

url(r'^getcenter/(?P<unique_id>[0-9]+/$', get_room_center, name='centroid'),