[postgis-tickets] [PostGIS] #2617: [raster] Enhanced mask object for raster map algebra

[PostGIS]

#2617: [raster] Enhanced mask object for raster map algebra
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 Reporter:  dustymugs    |       Owner:  dustymugs     
     Type:  enhancement  |      Status:  new           
 Priority:  medium       |   Milestone:  PostGIS Future
Component:  raster       |     Version:  trunk         
 Keywords:               |  
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Comment(by nclay):

 1. We are on the same page ALL  masks are valid except for irregular
 (jagged).
 {{{
 mask = [
 1,1,1,1
 1,1
 ]
 }}}

 Would be Invalid.

 2. Yes that was a kluge of an Idea, to add padding. However what came of
 it is that it, was an idea that it would be nice to have a way of
 expressing that you dont want a cell to be considered or returned at all.
 This has its limitations mainly to sparse masks and spatially irrelevant
 operations. An concrete example yet not very useful would be:
 {{{
 mask = [
 3.14,-,-,-,3.14
  -,-,-,-,-
 3.14,-,-,-,3.14
 ]
 poi = [3,2]
 }}}

 This would return a 1D  a  array containing the values from the four
 corners of the mask multiplied by their respective weights, also the value
 at the poi would be returned for the common case where you would like to
 poi -,+,*,/ aggregate function.

 This would be applicable to HAAT, where you are only really concerned with
 the values along 8 radials ( every 45 degrees ) from 2 to 16 km. Yes,
 currently you could pass in an mask array with nulls and receive a array
 with nulls in the respective positions but that is a lot of nulls to be
 only ignored when passed to an aggregate such as avg(). Why not through
 them out early on if the user explicitly ask for that? I would value your
 opinion on this.

 3. Again We're on the same page, except for the having the option
 explained in 2.

 4. Same as 3.

 Comment....
 I realized that wasn't right after I had sent that.... too late in the
 evening and not enough coffee. ;)

 Thanks,

 Nathaniel Hunter Clay

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Ticket URL: <http://trac.osgeo.org/postgis/ticket/2617#comment:5>
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