[postgis-users] Masking raster values

[Guido LEMOINE]

Dear List,

 

I am dabbling with some Landsat-8 imagery in PostGIS, using raster
functionality. I am primarily interested in deriving polygon-delineated
extracts from the various spectral bands (e.g. for a forest patch, an
agricultural field, etc).

 

Landsat-8 provides the so-called BQA band (see
http://landsat.usgs.gov/L8QualityAssessmentBand.php) which is a bit-coded
set of quality parameters, for which the cloud and haze indicators (bits
12-15 (right to left)) are the most important (for me). I would want to mask
out all pixels, in the spectral band(s), for which these bits are set in the
BQA band.

 

Did anyone come across a solution that would address this kind of masking
operation? The only reference I seem to be able to find is the statement
that "no masks (you can create a mask as a band)" in the WKTRaster wiki page
on osgeo, which is somewhat cryptic. I would know how to do this outside the
database (using JAI), but it seems that masking is some core operation one
would expect in raster functionality.

 

As a side issue, would it be possible (is it foreseen?) to create raster
operators that work in an equivalent arithmetic way as on single variable
(i.e. 2*rast, rast ~ 128, rast < 3) but produce rast as output (maybe
through a mapping to ST_MapAlgebra functions)?

 

Any pointers welcome and excuses if I have overlooked discussions on this
topic. 

 

Guido Lemoine

 

Scientific Officer

European Commission, Joint Research Centre (JRC)

Institute for the Protection and Security of the Citizen (IPSC)

Global Security and Crisis Management Unit

 

Via E.Fermi 2749, I-21027 Ispra (VA) Italy, TP 268

Tel. +39 0332 786239 (direct line) Fax +39 0332 785154

e-mail:  <mailto:guido.lemoine at jrc.ec.europa.eu>
guido.lemoine at jrc.ec.europa.eu 

web:  <http://globesec.jrc.ec.europa.eu/> http://globesec.jrc.ec.europa.eu

 

 

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