GeoNotes

I love this post thread so much I’m going to stick it into my blog. First because if you read into it and follow the links you can see the history of raster support in PostGIS (or reasons for lack thereof) for the PostGIS newbie readers. You can also see Paul’s encouragement and explanation of how this open source project works. Open Source developers develop stuff for their own needs. However, if you can make a well educated and clear argument for why they should spend their time putting your functionality into the project, they might just do it. Otherwise, they usually say, “it’s open source. code it yourself.”

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----- Original Message ----From: Paul Ramsey 
To: Pierre Racine 
Cc: warmerdam@pobox.com; nicolas.gignac@msp.gouv.qc.ca; smarshall@wsi.com; PostGIS Users Discussion 
Sent: Monday, July 14, 2008 10:11:05 PMSubject: Re: [postgis-users] PostGIS WKT Raster

Pierre,

Firstly, let me commend you for your understanding of the open sourcecommunity process! Not being shy, not taking “no” for an answer, andneedling the people you need to move are all excellent ways to keepthe wheels turning, particularly when done with good humor as you haveshown.  Other first timers could/should learn from your example!

So now I owe you a reply, no doubt:

You have gotten over my first hurdle, in that you have an actual usecase for raster, that is more involved than “I want to my images,because I hear database are faster”.

I have long thought that analysis, in particular a fusing of vectorand raster analysis was the only really compelling use case for rasterin database, so again, you’re on the side of the angels (me).

So, is your *design* good?

Probably as good as possible, but let me point out places of concernand see what you think:

- You propose to do this because their is a “great demand for it”, butthe great demand is generally the stupid demand for images-in-database“just because”. You must either somehow *stop* those people, or ensureyour solution is capable of meeting their needs.  Since you propose tomeet the demand, presumably you aim for the latter.  This *will*involve a good deal of non-analytical pre-processing infrastructure toconvert people’s multi-resolution, overlapping/underlapping filelibraries into a uniform resolution coverage.  I suggest you ignorethese people.- You are going to carry a certain amount of information into thedatabase and process data into bands, potentially for externalstorage.  Why not store external data in a format like TIFF that canhold all the bands and pyramids, etc?- Once you have the idea of external storage, you could as easily moveto internal storage with the BLOB interface.  Not that I recommendthis, it’s easier to back up and restore a filesystem of files than ahuge database full of BLOBs.- If you step back a bit and don’t even bother splitting up therasters into tiles, you can use an existing raster access library likeGDAL to work with serialized data.- Or you could use GRASS as your serialization format and hook intothat.  Added bonus: free algorithms.- Basically the less you muck with creating a “disk format for raster”(solved problem) and the more you muck with “integrating raster andvector analysis in SQL” (unsolved problem) the more leverage you willget.- I like your external storage idea. What are the implications forCREATE TABLE foo AS SELECT…?

Summary: your proposal is better than any I have seen, addressessolving problems that if solved will provide actual new functionalityand benefit to users, and clearly you’ve thought this through oversome time.

So, I look forward to seeing your initial plan of attack for development   

As you begin looking at the code base, you’ll find a few stubs ofraster support that Sandro built at my request for rasterizing vectorsinto CHIPs in the database… basically the first tip toe down thepath you have written up so completely.

Go with God.

Paul


On Mon, Jul 14, 2008 at 12:43 PM, Pierre Racine wrote:

 Paul Ramsey hasn’t yet said my design was:

 -a “meme” (http://blog.cleverelephant.ca/2008/06/x-my-l.html),

 -a “waste of time” (http://postgis.refractions.net/pipermail/postgis-devel/2007-July/002653.html)

-”useless” (http://postgis.refractions.net/pipermail/postgis-users/2007-May/015578.html)

 -that it was “pointless” (http://postgis.refractions.net/pipermail/postgis-users/2007-October/017250.html)

 -or that I was a “fool” (http://postgis.refractions.net/pipermail/postgis-users/2007-October/017239.html)

So I conclude it’s a good design!!!   

 He asked for a good design some time ago for raster in the database (http://postgis.refractions.net/pipermail/postgis-users/2006-October/013628.html)

 Where is the clever elephant?

 Pierre

—–Message d’origine—–

De : postgis-users-bounces@postgis.refractions.net

[mailto:postgis-users-bounces@postgis.refractions.net] De la

part de Pierre Racine

Envoyé : 7 juillet 2008 11:30

À : postgis-users@postgis.refractions.net

Cc : warmerdam@pobox.com; nicolas.gignac@msp.gouv.qc.ca;

smarshall@wsi.com

Objet : [postgis-users] PostGIS WKT Raster

Hi raster people,

I’m starting a 2-3 year project to develop a web-based application to

automate certain GIS tasks commonly needed in ecological research. The

tool will support queries over VERY large extent based on a Canada-wide

assemblages of raster and vector data layers. The queries will

typically

involve intersecting those layers with buffers defined around points or

transects.

We would like to implement this system with PostGIS, but it currently

does not to support raster data. We could convert all our data to a

single format (raster or vector) and use other tools, however PostGIS

seems to us the best and most powerful vector analysis tool available

and we would prefer to use it. We would like to develop a unified

toolkit so that the application mostly need not worry about

whether base

layers are in vector or raster format. We are then strong proponents of

having raster functionality in PostGIS. I have reviewed every thread on

this list on the subject. I have analysed them and I have compiled them

in the wiki

(http://postgis.refractions.net/support/wiki/index.php?RasterNotes).

The argument goes like this: The geodatabase paradigm has been a major

recent enhancement in GIS technology, I feel that the seamless

integration of raster and vector analysis should be one of the next.

Spatial analysis is emerging, beside the making and publishing of maps,

as one of the main desktop and web-GIS applications. Rastor/vector

seamless integration is already done for display (in most GIS and with

MapServer or ArcIMS on the web) but definitely not for

analysis. Desktop

analysts must still learn to use two distinct toolsets within most

(all?) GIS packages: one toolset for raster and another for

vector data.

Would not it be easier to build and use applications if we had a unique

data query and analysis toolset independent of the data model? I don’t

know any tool having this approach right now. A PostGIS foundation that

addressed this problem would offer better directions to application

developers than the dichotomic one proposed by ESRI since their

beginning. It would provide the necessary abstraction to develop GIS

with ONE set of analysis tools. I feel this is one good reason to

integrate raster in PostGIS. There is “GIS” in the word “PostGIS”.

PostGIS should then provide a COMPLETE GIS data foundation (read

“base”!) for geoapplication developers. I think Steve Marshall’s design

is a good step in this direction

(http://postgis.refractions.net/pipermail/postgis-users/2006-De

cember/01

4059.html).

At the same time, we would have a chance to reconsider the raster model

as a coverage instead of a series of images. Spatial databases got rid

of map sheets by allowing complete vector coverages to be stored as

single table (e.g. the entire United States) This approach should works

for raster data as well. Isn’t this the approach taken by ArcSDE?

In summary, I think we must stop thinking about PostGIS as a

mere vector

data repository to support mapping applications. This is the way most

objectors to raster integration seem to view it. We must think about

PostGIS as a powerfull indexed data analysis tool. Seamless

raster/vector analysis in the database could lead to a major

simplification of geoapplications.

I prepared a PowerPoint presentation with a complete specification of

raster in PostGIS and an analysis of what should be the result of

overlay operation between raster and vector layers. You can download

this PPT at: http://www.cef-cfr.ca/uploads/Membres/WKTRasterPostGIS.ppt

Please have a look at it, feel free to answer questions I ask and

comment.

Here are the main propositions of this design:

-Like a vector feature, rasters are stored as a subtype of “geometry”(a

new WKB/WKT geometry type called RASTER instead of POINT or POLYGON)

-There is no distinction between a raster and a tile. A tile

is a raster

and a table of rasters can be seen as a tile coverage. Hence, contrary

to Oracle GeoRaster, only one table is needed to store a coverage and

there is only one type.

-It support raster in the database AND raster out of the database. This

mailing list has shown that both approaches have their pros and cons.

Let’s not impose one approach over the other.

-It supports: multi-band, pyramids and variable nodata value, raster

size, pixel size and pixel type for each row.

-It supports import/export from/to Tiff and JPEG.

But moreover seamless raster/vector integration is materialized by

theses propositions:

-A lot of existing vector-only functions are adapted to work

with raster

also.

-Most new raster functions are also implemented to work with vector.

Only basic raster derivation functions are proposed.

-Most vector/vector existing functions are adapted to work seamlessly

with raster/vector or raster/raster

I also want to ask:

-What is the status of PGRaster? Is any development now underway?

We have some resources to devote to this project over the next

few years

and are very interested in forming collaborations to move this work

forward.

Pierre Racine

GIS/Programmer Analyst

University Laval

http://www.cef-cfr.ca/index.php?n=Membres.PierreRacine