Comments on: Rasters in the Database—Why Bother?

By: Khavin Sivenandan

Khavin Sivenandan — Wed, 13 Aug 2008 15:16:15 +0000

Hi there, is there any plugin for Qgis which can be utilised to export rasters to Postgis?

By: Luc

Luc — Sat, 08 Mar 2008 09:51:09 +0000

The best solution I’ve come across so far has been tiles at different resolutions through WMS or WCS, flexibility is the keyword in this case for me…

By: Tim Bowden

Tim Bowden — Sun, 17 Feb 2008 16:28:02 +0000

@Josh, I can see where you’re coming from, and at first look the sql model does look attractive. I still believe it’s a blind alley though.

What you’re really asking for is a web interface to something like GRASS, and wondering if it wouldn’t be easier to re-implement GRASS in an rdbms to get it. For my money, web enabling GRASS (or equivalent) is the least cost path, even at 100:1.

By: Josh Campbell

Josh Campbell — Sun, 17 Feb 2008 05:00:05 +0000

@Tim, thanks for the info. I can understand the image data argument, but I’m thinking about a hydrologic model that would run through a web application. A user would access a web page that contained a map view of an area and select a location for analysis; a set of independent variables would be created for that location (first step is to derive a watershed boundary for the newly selected point and use that boundary as a mask for subsequent zonal statistics). The watershed delineation requires a digital elevation model and the zonal statistics run on multiple other non-image rasters.

Given the number of vector ‘overlay’ operations now available within the rdbms, I wondered if raster calculations could be structured as sql queries?
Thanks,

By: Tim Bowden

Tim Bowden — Sat, 16 Feb 2008 06:21:36 +0000

@Josh Campbell, the access method is independent of how you use the image data. Rule of thumb, if somebody recommends storing image data in an rdbms, they don’t know what they are talking about. Yes, there are a few esoteric cases where it may make sense, but that’s far from the norm. IMHO the map algebra function argument only makes sense if the rdbms does the algebra, and for some reason it’s more efficient than doing it on a fat client. What rdbms and what algebra functions did you have in mind?

By: Dave Smith

Dave Smith — Fri, 15 Feb 2008 21:28:26 +0000

Oracle GeoRaster, ESRI Image Server, seems a puzzling question as to the relevance anymore. The only real value any of these could potentially deliver over simply serving up cached tiles would be in on-demand web-based image analysis and processing, but if this is the case, why not DIPEX or other solutions?

Seems like trying to turn a niche into mainstream when it’s not warranted.

By: Josh Campbell

Josh Campbell — Fri, 15 Feb 2008 20:30:27 +0000

Could someone comment on the best raster storage and access methods for web geoprocessing? I’m wondering if having the rasters in a database would be good for map algebra functions?

By: Sean Gillies

Sean Gillies — Fri, 15 Feb 2008 19:48:33 +0000

I should know by now that tile == static to most people. I’m just thinking of raster pieces, static or dynamic as needed, served from an HTTP server. WMS and WCS pretty much get the job done, granted, but are smelly. I’ve made the arguments many times in many other places, so here I’ll just say “smelly”.

By: Matt Perry

Matt Perry — Fri, 15 Feb 2008 19:08:53 +0000

@Sean: tiles work for static aerial imagery served up under a pre-determined coordinate systems and resolution. What about non-imagery raster data? What about cases where you need the raw data as a contiguous raster? What about resampling methods? Other projections? Resolution? Edge effects? Tiles rarely work for me but I guess if all you need is base aerial photos it would work.

As far as spanning different machines, you could nfs mount them and create a tile index across the different machines. I haven’t tried this

By: James Fee

James Fee — Fri, 15 Feb 2008 19:07:57 +0000

Paul, it will probably take years for folks to get it out of their system.