[postgis-users] Re: Enormous file geodatabase feature class

[dnrg]

Thanks Regina and Webb. Regina, do you actively use
PostGIS for City of Boston GIS work?

Although I now live in NC, I was born and raised in
New England. Only moved from Boston (Somerville) to
North Carolina in 2001. Used to work for Federal DOT
in what some call "The Klingon Building" (Volpe Center
in Kendall Square MIT, behind the Marriott. Never
realized DOT's "tri-scallion" logo was the same as a
Klingon symbol until some waiter with a Klingon tattoo
pointed it out to me one day. "Oh yeah, you work in
the Klingon building." Well, cool.

> Have you thought about using inherited tables and
> constraint exclusion. It has a couple of advantages
> over loading everything in one table
> 1) Your master table can have fewer fields than the
> other tables, that way you can have the core fields
> in master and still maintain some of
> the other fields for the counties that vary.

Haven't thought about it, but thanks to you I now
am--thanks for the suggestion. Is this something
you've actively used? Can you give a real-world
example? Have any others here used inherited tables in
this way, and can you give an example?
  
> 3) With constraints in place that constrict the
> bounding box of each county or by county code or
> whatever, your queries will be much more efficient.
> I presume most of the time you'd be looking at a
> particular region. 

The typical map scale for the user would be zoomed
into an individual parcel.
  geodatabase feature class

Webb, you wrote: 
> more funding, right?) is a general  script that 
> calls county specific filters to standardize the
> input on its way to the big table; then
> when you get a new county's worth of data you just
> write a new filter
> specification (I can imagine a config-like syntax
> that specifies input

Also a good idea, thanks. A colleague at work does
something similar using a text file of county-specific
column mappings and processes that in VB code within
ArcMap or ArcCat. It's all space delimited and looks
rather ugly to me (because I don't know the code I
suppose).

> column, output column, and function to convert if
> necessary, or some
> such) and call it in the big script.  You can store
> the filters specs
> systematically in the database too, similar to the
> way postgis stores
> proj command lines in the spatial_ref_sys table.

Well hell yeah. *That* I like; storing as much as
possible in the DB vs. futzing with a text file. Could
use pickling in Python, but I'm a fan of putting as
much as possible in the DB.
 
> Postgis doesn't play nice with rasters, so you may
> have vectorize them somehow if you are going to do
> SQL with such data. Somebody who knows more than me
> should chime in here.

For the raster wind class data, that will be
summarized per parcel using zonal statistics (each
parcel will be a zone) and added as attributes to the
parcel data, e.g. MIN, MAX, MODE, MEDIAN, etc.

I'm planning on pre-calculating those values as each
county's parcel data goes into PostGIS.

My question is this: in the past, I've used ArcGIS
Spatial Analyst extension to create zonal statistics.
Can GRASS, or some other FOSS tool, do zonal
statistics? Or is there a zonal statistics function in
PostGIS? (in which case, I would need to store rasters
in PostGIS, but only for analysis). 

Would be nice to be able to do on-the-fly analysis,
where a person could draw a polygon, based on, say,
some Google Maps API imagery, around their parcel
where I was unable to obtain parcel data from a
particular county.
 
> If you put up a wiki or anything let the list know,
> and if you do
> something big refractions would probably be
> interested in a case
> study.

Will do.

Finally, here's a dumb question on FOSS generally:

I understand RMS's "free, as in freedom" / libre view
of open source--meaning the GPL's enforcement of the
right to tinker with code all down the line with
derivative works.

When FOSS people instead say, "free, as in free beer"
do they mean MIT/X-type licenses? Or is that simply a
phrase RMS uses to frame what the GPL is / is not?

Or does "free, as in free beer" not have anything to
do with open source at all? e.g. free, like the way
SQL Server Express or ArcGIS Explorer are free--free
of cost, but no access to the source code. 

Don't want to get into a Holy War here, just trying to
understand the distinctions.





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