Monday, July 25, 2011

Simple gvSIG Jython Console script to list layers in a Map View

I have always wondered how to use the Jython Console in gvSIG. There isn't much published documentation on using it or perhaps I simply were not very good in finding it. In any case, I managed to figure out how to access and use the gvSIG objects from within the Console window. To illustrate, I wrote a simple Python script that simply gets a pointer to the active Map View window and then loop through the list of loaded layers and print out the name and number of records for each layer.

Below is the example code listing and saved to a script file test.py.


#import gvSIG library
from gvsiglib import *

#get the map view
mapview = gvSIG.getActiveDocument()
#get the map control
mapctrl = mapview.getMapControl()
#get the map context
mapctx = mapctrl.getMapContext()

#print the list of layers in the map view and the record count for each layer
for i in range(mapctx.getLayers().getLayersCount()):
    layer = mapctx.getLayers().getLayer(i)
    rs = layer.getRecordset()
    print "%s,%d records" % (layer.getName(), rs.getRowCount())

  1. Start up gvSIG OADE 2010. Open a Map View. Load in a couple of layers e.g. BLDG.shp and layer1.shp.


  2. Select File | Scripting | Jython Console.

    The Jython window appears.

  3. At the Jython prompt, type in: execfile ("c:/temp/test.py").

    The script is loaded and executed listing out the layers and the number of records.
Instead of loading from a script file, the Jython Console can accept typing in the code line by line in the Console prompt. However, I find using a script file is more convenient. 

After the gvsiglib has been imported into the Console, it is possible to access the gvSIG objects and make use of the auto-completion capabilities of the Jython Console to explore the object methods and properties as shown in the screen shot below.

Monday, July 18, 2011

Google Gadget for monitoring UK earthquakes


This gadget will allow you to subscribe to the British Geological Survey (BGS)'s recent UK earthquake GeoRSS feed. It shows the latest earthquakes as color coded (by depth and age) icons with tool tips on a Google Maps backdrop - the older the earthquake, the more transparent the icon will look.

The gadget has a list tab which displays the earthquake information as a text list with hyperlinks for more details - the list can be sorted by the earthquake magnitude, depth as well as the date-time. Using the list, you can easily find and locate the largest, the latest or the deepest earthquakes.

You can leave this gadget on the screen and it will update itself as it receives the latest feed. Upon receiving the data, it will automatically zoom to the latest earthquake epicenter. Clicking on an earthquake icon will bring up more information about the earthquake from the BGS site.

Monday, July 11, 2011

Connecting GeoMedia Professional to a read/write PostGIS database warehouse

Intergraph has released an open source GeoMedia PostGIS data server under the Apache 2.0 license on this site http://geomediapostgis.codeplex.com/. I downloaded and tried out creating and connecting to a read/write PostGIS warehouse on a Windows server from a remote client using the sample GeoMedia workspace USSampleData.gws. The instructions on the binaries talked about using Debian Linux as the host for the PostGIS database while I used Windows XP as the host instead.

Installing PostGIS 1.5 onto PostgreSQL 9.0 on Windows
After installing PostgreSQL 9.0 on Windows using the packaged installer on my server, I did the following:
  1. Download the PostGIS 1.5 Windows binaries from http://postgis.refractions.net/download/windows/pg90/postgis-pg90-binaries-1.5.3.zip
  2. Extract the files into a folder e.g. C:\Program Files\postgis-pg90-binaries-1.5.3.

  3. Use a text editor and open up the makepostgisdb.bat file.

  4. If necessary, change the PGPORT, PGHOST, PGUSER, and PGPASSWORD settings to match the Windows PostgreSQL installation.
  5. Uncomment the last line to create the database defined by the THEDB setting as a template PostGIS database e.g template_postgis15. Close and save the file.

  6. Run the batch file makepostgisdb.bat.

    PostGIS is installed and a template database is created.
Configure PostgreSQL for network access
By default, PostgreSQL is configured not to accept any network database requests. I had to do edit the configuration parameters to allow network access.
  1. On the server, select Start | All Programs | PostgreSQL 9.0 | pgAdmin III.

    The pgAdmin III application appears.
  2. In the Object browser pane, double click on the PostgreSQL 9.0 (localhost:5432) node. Enter the password if prompted.

    Connection to the server is established.
  3. Select Tools | Server Configuration | pg_hba.conf.

    The Backend Access Configuration Editor appears.
  4. Double click the empty last row.

    The Client Access Configuration dialog appears.
  5. Toggle Enabled on. Choose host for Type, all for Database, all for User and md5 for Method. Type in an appropriate IP Address for your network e.g. 192.168.8.0/24.

    Note: In this example, I am allowing access for any clients with the IP address pattern 192.168.8.*.
  6. Click OK.
  7. Select File | Save. Press Yes if prompted.
  8. Select File | Reload Server. Press Yes if prompted.
  9. Close the Client Access Configuration and Backend Access Configuration dialogs. 
Create and configure the Postgis database
  1. In the Object browser, expand and select Login Roles node.
  2. Select Edit | New Object | New Login Role.

    The New Login Role dialog box appears.
  3. In the Role Name field, type in gdouser. In the Password and Password(again) fields, type in gdouser.

  4. Click OK.

    The login is created.
  5. In the Object browser, select the Database(s) node.
  6. Select Edit | New Object | New Database.

    The New Database dialog box appears.
  7. In the Name field, type in gdotest. Choose gdouser as the Owner. Choose template_postgis15 as the Template.

  8. Click OK.

    The database is created.
Configuring the PostGIS GDO server on the client
  1. On the client machine, I downloaded the PostGISGDObin.zip package from http://geomediapostgis.codeplex.com and extracted to a folder e.g. C:\Program Files\PostGISGDO\.

  2. Run Register.bat.

    The data server is registered with GeoMedia.
  3. Double click the file PsgDBUtils.exe.

    The PostGIS GDO Database Utilities appear.
  4. Click New Connection.

    The New Connection dialog box appears.

  5. In the Server field, type in the address or name. In the Database field, type in gdotest. In the User field, type in gdouser. In the Password field, type in gdouser. Click OK.

    The utility is connected to the PostGIS database.
  6. Click Create INGR Metadata Tables.

    The metadata tables are created.
  7. Click Run script.

    The Open dialog box appears.
  8. Browse and choose the file USSampleProjCS.sql. Click Open. Click OK when prompted.

    Note: this script will add the Albers Equal Area coordinate system to the PostGIS database for working with the sample USSampleData.gws workspace.
  9. Click Close.
Connect to the PostGIS database from GeoMedia
  1. Start GeoMedia and open up the sample workspace USSampleData.gws.
  2. Select Warehouses | New Connection.

    The New Connection dialog box appears.
  3. Choose PostGIS Connection Type.
  4. In the Server field, type in the IP address or node name of the PostGIS server.
  5. In the Database field, type in gdotest.

  6. In the User and Password fields, type in gdouser. Click OK.

    GeoMedia is connected to the PostGIS database.

    Note: You should now have full read/write access to the PostGIS database.

Monday, July 4, 2011

Convert raster to vector polygons with Global Mapper

Global Mapper 12 has a function tuck away in a pop up menu to convert a grid layer or image layer into vector polygon features. It's the Create Area Features from Equal Values in Selected Layer accessible from the Overlay Control Center's right click pop up menu. Using this function is straightforward - simply load in a grid layer, fill in some parameters, and run the command.

To show how this works, see the example below in which a forest cover ArcGrid ASCII file is vectorized into a polygon vector layer at 10% cover interval.
  1. Start Global Mapper. Load in a grid layer e.g. Cov.asc


  2. Select ALT+C.

    The Overlay Control Center is displayed
    .
  3. In the Overlay Control Center, mouse right click on the grid layer.

    A pop up menu appears.

  4. Choose Create Area Features from Equal Values in Selected Layer.

    The Setup Equal Value Area Creation dialog box appears.

  5. Optional. Change the Layer Description, Value Attribute Name, or Area Classification.
  6. In the Maximum Match Distance field, type in a value e.g. 0.05.

    Note: The example grid layer cell values are actually in %, even though the screenshot shows meters. It's just that Global Mapper assumes all grid layers are elevation related layers.
  7. Click OK.

    The vector polygons are generated.


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