Hi
In my project
https://sourceforge.net/p/treintaytres/code/HEAD/tree/trunk/code_files/data_storage/ I have the
table
TABLE_SCHEMA TABLE_NAME DATA_TYPE TYPE_NAME COLUMN_NAME
treintaytres topo_files␟t 1111 uuid id
treintaytres topo_files␟t 93 timestamptz entry_pit
treintaytres topo_files␟t 1111 uuid source_id
treintaytres topo_files␟t 12 text file_name
treintaytres topo_files␟t 1111 raster tile
treintaytres topo_files␟t 93 timestamptz
file_creation_pit
treintaytres topo_files␟t 12 text file_hash
TILE contains topographical height raster data from OpenTopography.
They are from different regions, let's say, some tiles cover
Switzerland, some cover New Zealand. I want to create slope and other
data from the height data and I have some questions I hope you can
answer or point me to answers.
a) Is it more efficient to convert the raster to vector data and
calculate on the those than to calculate directly on the raster?
b) To my understanding, if I calculate the slope on a raster tile, the
slope,… of the borders will have accuracy problems. My I idea, was to
"stitch" a tile with its direct neighbours, calculate on the composed
tile, and either save a cropped calculated composed tile to its
original dimension or save the calculated composed tile as is,
probably the latter.
Can I compose as follows?
with RASTER_NEIGHBORS as ( select R1.TILE as CURRENT_TILE
,R2.TILE as NEIGHBOR_TILE
,R1.ID as CURRENT_ID
from TOPO_FILES␟T R1
left outer join TOPO_FILES␟T R2
on ST_Touches(R1.TILE
,R2.TILE)
or ST_Intersects(R1.TILE
,R2.TILE)
where TRUE
--and R1.ID =
'6b8ca53a-bb5f-4c2b-a9c9-94b6a706e9b0'
and TRUE)
,NION as (select CURRENT_TILE as TILE
,CURRENT_ID
from RASTER_NEIGHBORS
union
select NEIGHBOR_TILE as TILE
,CURRENT_ID
from RASTER_NEIGHBORS)
select ST_Union(TILE) as COMPOSED_TILE
,CURRENT_ID
from NION
group by CURRENT_ID;
c) Finally, I want to select all the areas where slope, TRI,… conform
certain criteria and have a minium surface size. Do I do it this
better on vector data and do I need to do this on data composed of all
the contiguous areas?
I would be grateful for any nudge into the right direction. Maybe URLs
with samples.
Kind regards
Thiemo
