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Re: [udig-devel] Seeking more direction from the uDIG community
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Question for Cory;
Can we let the PostGisGeoResource resolve to a the JDBC connection pool?
That way Mr Richardson can just start coding with JDBC (which he appears
to be comfortable with).
Jody
Hello Community,
Thanks for previous help you've offered. I could use a bit more
direction if possible to determine whether I should carry on with uDIG
for a small project I am working on. I'm finding the uDIG development
learning curve to be a bit steep so far.
I've spent the last few days looking at uDIG (e.g. plugin tutorial and
all the other online resources) and I am trying to figure out the
simplest way to make use of powerful postgreSQL/postGIS capabilities.
Previously I was concerned with constructing spatial queries on
massive point data sets. These processes are easy if I use a standard
postgreSQL interface like psql or pgAdmin. It seems like it should be
a fairly simple task to construct plugins within uDIG that make use of
these and other RDBMS capabilities through JDBC (if they don't already
exist somewhere). I read an entry on Cory Horner's community page
about extending uDIG functionality to incorporate better RDBMS
capabilities. I am most definitely interested in this because I am
always faced with problems where this type of capability would be an
asset.
To give you an idea of the type of functionality I am interested in,
considering the following two examples:
(1) I am constantly using GIS and RDBMS capabilities separately
(loosely coupled fashion)for information management in the field of
hydrology. For example - I need to summarize the joint probability
distribution of land-use and soil types to determine an average
(lumped) runoff coefficient for nested watersheds (since runoff is a
function of landuse and underlying soil properties, among other
things). I do this by exporting the polygon intersection of a soils
layer, land-use layer and watershed layer to a RDBMS. Then I use
lookup tables to determine coefficients for individual landuse-soil
combinations and use an aggregate query to determine the mean value
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Subject: Re: [udig-devel] Seeking more direction from the uDIG community
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Thanks Jesse,
Are there some coded examples on working with geotools? I don't see
exactly how I can execute queries on multiple layers using QUERY and
DATASTORE objects, although it's obviously possible from what you say.
I think getting the database connection and generating custom SQL would
be most flexible, even if it's not very slick. Also, in some cases I
work with massive point files (posted a question about this a couple
days ago) and I think it would be better to have spatial queries done on
the server side. Similarly with time-series data it is often necessary
to add temporary columns, iterate through the table several times and
perform some calculations. Given this I would happily take you up on
some details to go this route, if it isn't too much trouble for you...
On the other hand, I may find this gets over my head fairly quickly and
just have to implement these ideas without using uDIG for anything
accept for viewing outputs!
Murray
Jesse Eichar wrote:
Right now a layer is a table in postGIS. Using the QUERY object and a
FeatureStore from the layer, it is possible to obtain features from that
table with the attributes you specify in the query. The types of
queries that can be created can be very complex and can use many spatial
operations. However the datastore is primarily an Access/Query object
that allows access to the features in the PostGIS (or more generally the
data source what ever it may be) for viewing or direct editing. There
isn't an API for adding columns but there is one for creating new tables.
There is not yet an OPERATIONS API yet in Geotools, which is likely what
you are looking for. There are currently 2 ways to do what you require
that I can think of:
1. In order to satisfy your requirements on the server side you would
have to get the Database connection and generate custom SQL queries and
execute them.
2. You can fetch the features to the client using the Datastore API and
its queries, and do the calculations on the client and write the result
back to the PostGIS, also using the Datastore API.
As far as I can tell you can do most of these steps using the second
method. As I said Queries (and Filters) can do some very complicated
work including GeoSpatial and other "normal" queries. Intersection,
differences, etc... can all be done server side using Filter and Query.
If you want more details on any of these steps let me know,
Jesse
On 10-Jan-07, at 9:32 AM, Murray Richardson wrote:
Hello Community,
Thanks for previous help you've offered. I could use a bit more
direction if possible to determine whether I should carry on with uDIG
for a small project I am working on. I'm finding the uDIG development
learning curve to be a bit steep so far.
I've spent the last few days looking at uDIG (e.g. plugin tutorial and
all the other online resources) and I am trying to figure out the
simplest way to make use of powerful postgreSQL/postGIS capabilities.
Previously I was concerned with constructing spatial queries on
massive point data sets. These processes are easy if I use a standard
postgreSQL interface like psql or pgAdmin. It seems like it should be
a fairly simple task to construct plugins within uDIG that make use of
these and other RDBMS capabilities through JDBC (if they don't already
exist somewhere). I read an entry on Cory Horner's community page
about extending uDIG functionality to incorporate better RDBMS
capabilities. I am most definitely interested in this because I am
always faced with problems where this type of capability would be an
asset.
To give you an idea of the type of functionality I am interested in,
considering the following two examples:
(1) I am constantly using GIS and RDBMS capabilities separately
(loosely coupled fashion)for information management in the field of
hydrology. For example - I need to summarize the joint probability
distribution of land-use and soil types to determine an average
(lumped) runoff coefficient for nested watersheds (since runoff is a
function of landuse and underlying soil properties, among other
things). I do this by exporting the polygon intersection of a soils
layer, land-use layer and watershed layer to a RDBMS. Then I use
lookup tables to determine coefficients for individual landuse-soil
combinations and use an aggregate query to determine the mean value
for each watershed. It is nice to then join the mean value back to
the watershed layer and display this in a map. I also use the RDBMS
to do reporting of the individual intersected polygons by watershed.
This type of analysis and reporting is standard in flood risk
assessment and could be very easily streamlined with a tool like uDIG
and postgreSQL.
(2) Storing and accessing spatial-temporal hydrology data is an
emerging area of interest (consider the ESRI ArcHydro framework if
you're familiar with it) and an interesting direction for Open Source
GIS. For example, I would like to be able to store decades worth of
hourly streamflow data for numerous gauged weirs within a postgreSQL
DB and have this linked to a uDIG application that allows me to
extract the streamflow data by (e.g.) clicking on a point station and
entering a date. The query result could be just exported to a text
file for now. This capability would open the door to a whole range of
interesting spatial-temporal hydrology applications (e.g. recession
analysis, climate and streamflow data interpolation, hydrologic model
parameterization).
Based on these two particular examples, could someone perhaps direct
me on how to proceed to develop a very simple proof of concept for
enhanced RDBMS capabilities within a GIS environment? Consider
example 1 for instance - can I create a uDIG operation that is
accessed by right-clicking on 3 highlighted layers (like the
difference operation that is available when two layers are selected).
For my purposes I would like these to be postGIS layers. The
operation could then execute the postGIS intersection procedure, the
attribute join and the aggregate function all within the postgreSQL
service, and then map the results back to the watershed layer for
display in uDIG?
I know this is a fairly specific question, but what it boils down to
is, how do I access postGIS spatial operations as well as general
postgreSQL RDBMS functionality and non-spatial tables within the uDIG
environment?
Thanks in advance for any help. This project is for a small Open
Source/Open Access Student Experience program grant I am working on
through University of Toronto that involves developing a
proof-of-concept idea and some educational tutorials using
postgreSQL/postGIS. I would like to eventually be able to post the
results on my own uDIG community page if things go well. I think this
type of work could help open up uDIG capabilites to the slightly less
technical users like myself (e.g. GIS and basic programming/RDBMS
skills experience, but still need lots of examples and explicit
documentation to follow!).
Look forward to hearing back from someone - hope it's not too much to
ask over a mailing list!
--Murray Richardson, M.Sc
PhD Candidate
University of Toronto
murray.richardson@xxxxxxxxxxx
_______________________________________________
User-friendly Desktop Internet GIS (uDig)
http://udig.refractions.net
http://lists.refractions.net/mailman/listinfo/udig-devel
_______________________________________________
User-friendly Desktop Internet GIS (uDig)
http://udig.refractions.net
http://lists.refractions.net/mailman/listinfo/udig-devel
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