[postgis-devel] [PostGIS] #2122: [raster] Real extent feature lost after metadata as views

[Mateusz Loskot]

On 1 December 2012 18:58, Bborie Park <dustymugs at gmail.com> wrote:
> On Sat, Dec 1, 2012 at 8:03 AM, Sandro Santilli <strk at keybit.net> wrote:
>> On Sat, Dec 01, 2012 at 12:20:13AM +0000, Mateusz Loskot wrote:
>>
>>> Blocking is a generic technique, almost equally important
>>> as pyramids. We can't simply ignore it.
>>
>> Sorry if I ask it again (I think I didn't get an answer to that):
>> is padding _necessary_ to implement "blocking" ?
>>
>
> According to my impression of the spec, yes.  Padding is in essence
> rule #1 where every tile must have the same size.
>
> http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking01

Padding a realisation of the requirement of regular grid of tiles.

>> In other words, is it really a problem if tiles exist which are
>> _smaller_ than the "official" tile size ? Why do you need NODATA
>> values rather than just NO values at all ?
>>
>> I'm probably missing something but really can't see that need.
>>
>> I'm trying to understand this because having no padding at all
>> would solve the issue, in that the computed extent could be same
>> as the original extent...
>>
>
> I'm a proponent of letting the user decide.  Just use the -r flag of
> raster2pgsql to specify that tiles should be padded.  If -r flag isn't
> set, don't pad.  That way the extent in raster_columns is an accurate
> extent of the space covered by the set of tiles in a table.

The first part of this proposal is clear, but the part starting with
"That way the extent in raster_columns is an accurate extent" is not.
AFAIU, that depending on use of -r and padding appended or not,
the actual spatial extent will vary, won't it?

Could you work it through based on the example from the ticket,
for 512x512 utm.tif raster?

raster2pgsql -C -t 300x300 public.utm300 utm.tif

versus

raster2pgsql -C -r -t 300x300 public.utm300 utm.tif

What is the pixel space of the public.utm300 table?
What is the spatial extent of the public.utm300 table?

Best regards,
--
Mateusz Loskot, http://mateusz.loskot.net