[postgis-users] Help with ST_CLIP

[Simon G Greener]

Stephen,

A type 4326 not 4236.

 > select st_astext(geog::geometry) from gbr_marine_park_boundary;

The numbers look correct after the cast.

Even though the data is extensive should I consider transforming to a 
projected SRID?

Geographic rasters are not supported right? This is the reason for the 
cast to call the ST_Clip function.

regards

Simon

On 13/03/2021 5:42 am, Stephen Woodbridge wrote:
> Hi Simon,
>
> A geography column in 4236 sounds strange. Check the coordinate values 
> of the cast polygon.
>
> select st_astext(geog::geometry) from gbr_marine_park_boundary;
>
> and see if they look like what you expect.
>
> -Steve W
>
> On 3/12/2021 1:37 AM, Simon SPDBA Greener wrote:
>> "POSTGIS=""2.4.3 r16312"" PGSQL=""100"" GEOS=""3.6.2-CAPI-1.10.2 
>> 4d2925d6"" PROJ=""Rel. 4.9.3, 15 August 2016"" GDAL=""GDAL 2.2.3, 
>> released 2017/11/20"" LIBXML=""2.9.4"" LIBJSON=""0.12.1"" 
>> LIBPROTOBUF=""1.2.1"" RASTER"
>>
>> I have a polygon that defines the boundary of the Great Barrier Reef.
>>
>> A) That boundary is stored as a vector geography column (4326) in a 
>> table.
>> B) I have loaded a raster dataset of depths (4326) and checked its 
>> statistics.
>>     The data loaded correctly and I can see valid depth values.
>>
>> Now I want to clip the data in B with the polygon in A.
>>
>> (I can't use a raster function with a geography object so I cast it 
>> to geometry.)
>>
>> create table gbr100x100clip
>> as
>> select ST_Clip(g.rast, 1, m.geog::geometry, false) as rast
>>   from gbr_marine_park_boundary as m,
>>        gbr100x100 as g;
>>
>> This works but the value (depth) of the whole (slipped) rasters is NULL.
>>
>> I expected to see depth values but this returns null values.
>>
>> SELECT (stats).*
>>   FROM (SELECT ST_SummaryStats(rast, 1) As stats FROM gbr100x100clip) 
>> As foo
>>  order by max desc;
>>
>> Can anyone give me an idea of what I am doing wrong?
>>
>> regards
>> Simon
>>
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>
>