How can I change the "NoData" value for a raster column in PostGIS?

Question

I have a raster column with "NoData" value of 3.40282346638529e+038 in PostGIS. I want to change the NoData value to 100. I used the following code:

SELECT ST_Reclass(ukc,1,'3.40282346638529e+038:100', '32BF', 3.40282346638529e+038) rast
INTO for_delete1
FROM raster_table

but it changed all pixel values to 3.40282346638529e+038 and it changed non of the NoData pixels!! then, I used the same query and just changed '3.40282346638529e+038:100' to '100:3.40282346638529e+038'. This one also made some strange changes but the NoData value is still the same.

How can I change the NoData value for a raster column in PostGIS?

Answer 1

I found the solution. In fact the third input of ST_Reclass() should be two sets of range not single values. So I changed it to:

SELECT ST_Reclass(ukc,1,'3.40282346638529e+037-3.50282346638529e+038:100, -20-20:-20-20', '32BF') rast
INTO for_delete1
FROM raster_table

This Code finds the values between 3.40282346638529e+037 and 3.50282346638529e+038 and then change them to 100. In addition, it map the values between -20 to 20 to the same range because the pixel values are between -20 and 20. Thus, the pixel values are not changed and the NoData value is changed to 100.

At the end, the NoData value should be defined for the column by:

UPDATE for_delete1
SET rast = ST_SetBandNoDataValue(rast, 1, 100::double precision);

This way, PostGIS knows that 100 will be considered as the new NoData value.