[postgis-users] getting raster values for point from st_value

[Jason Mathis]

Hi Pierre,

Thanks so much for super quick response. You will have to forgive me I am fairly new to postgis. 

Creating the table is no problem but how would I check if it overlaps with my points? 

thanks!


On May 13, 2014 at 4:08:40 PM, Pierre Racine (pierre.racine at sbf.ulaval.ca) wrote:

Create a new table with the extents of the raster tiles and check if it overlaps with your points:  

CREATE TABLE rastextets AS  
SELECT rast::geometry  
FROM tbl_raster  

Pierre  

> -----Original Message-----  
> From: postgis-users-bounces at lists.osgeo.org [mailto:postgis-users-  
> bounces at lists.osgeo.org] On Behalf Of Jason Mathis  
> Sent: Tuesday, May 13, 2014 5:56 PM  
> To: postgis-users at lists.osgeo.org  
> Subject: [postgis-users] getting raster values for point from st_value  
>  
> Hi all,  
>  
> I have recently loaded a good amount of rasterized shape files into a db. I  
> mainly used gdal_rasterize and raster2pgsql. The shape files were in NAD83  
> so I used the below commands to rasterized and load.  
>  
> gdal_rasterize -at -a desc -where "desc='Very High'" -burn 2 -tr 30 30 -ot  
> byte -a_nodata -99 shape_file.shp raster.tiff  
> raster2pgsql -d -s 5070 -t 100x100 -F -I -C -Y raster.tiff tbl_raster | psql -d  
> raster_db  
>  
> I had two sets of shape files one set had about 10 burn values and another  
> had about 50. The issue is getting these values out of the raster. I believe I  
> should be using something from this page:  
> http://postgis.net/docs/RT_ST_Value.html.  
>  
> I can visualize this file in QGIS and it looks good, the histogram shows  
> values. I can also use the postgis functions, st_summarystats or  
> st_histogram to see some data but I need to be able to query a given point  
> and return the raster value.  
>  
> I have this:  
>  
> SELECT ST_Value(rast,(ST_Point( -111.750185, 34.886948)))  
> FROM tbl_raster  
> WHERE st_intersects(rast, (ST_Point(-111.750185, 34.886948)))  
>  
> Then i thought oh wait should I set the srid?:  
>  
> SELECT ST_Value(rast,(ST_SetSRID(ST_Point( -111.750185,  
> 34.886948),5070)))  
> FROM tbl_raster  
> WHERE st_intersects(rast, (ST_SetSRID(ST_Point(-111.750185,  
> 34.886948),5070)))  
>  
> Still I get nothing, then I thought I need to transform so I got this:  
>  
> SELECT ST_Value(rast,(ST_Transform(ST_SetSRID(ST_Point( -111.762866,  
> 34.874309),5070),4326)))  
> FROM tbl_raster  
> WHERE st_intersects(rast, (ST_Transform(ST_SetSRID(ST_Point( -  
> 111.762866, 34.874309),5070),4326)))  
>  
> But in the end nothing.  
>  
> I did need to add the SRID to the spatial_ref_sys table:  
>  
> INSERT into spatial_ref_sys (srid, auth_name, auth_srid, proj4text, srtext)  
> values ( 5070, 'EPSG', 5070, '+proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=23  
> +lon_0=-96 +x_0=0 +y_0=0 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0  
> +units=m +no_defs ', 'PROJCS["NAD83 / Conus  
> Albers",GEOGCS["NAD83",DATUM["North_American_Datum_1983",SPHER  
> OID["GRS  
> 1980",6378137,298.257222101,AUTHORITY["EPSG","7019"]],TOWGS84[0,  
> 0,0,0,0,0,0],AUTHORITY["EPSG","6269"]],PRIMEM["Greenwich",0,AUTHORIT  
> Y["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG  
> ","9122"]],AUTHORITY["EPSG","4269"]],PROJECTION["Albers_Conic_Equal_  
> Area"],PARAMETER["standard_parallel_1",29.5],PARAMETER["standard_par  
> allel_2",45.5],PARAMETER["latitude_of_center",23],PARAMETER["longitude  
> _of_center",-  
> 96],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["  
> metre",1,AUTHORITY["EPSG","9001"]],AXIS["X",EAST],AXIS["Y",NORTH],AUT  
> HORITY["EPSG","5070"]]’);  
>  
> But ultimately I have nothing I can’t seem to get any data out using a query  
> with a point value. I am thinking it has to do with the srid? Since I can  
> visually inspect it and see data.  
>  
> Anyone have any hot ideas as to why I am not seeing data?  
>  
> Thanks!  
>  
>  
>  
> This transmission contains confidential and privileged information intended  
> solely for the party identified above. If you receive this message in error,  
> you must not use it or convey it to others. Please destroy it immediately  
> and contact the sender at (303) 386-3955 or by return e-mail to the sender.  

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