I have a raster map (-100 to +100) and I need to get all the minus values as absolute values (-100=100; -99=99…). How can I do this? Is it something like reclassify?
QGIS – How to Get the Absolute Value of a Raster Cell
qgisreclassify
Related Solutions
Use the Add Entry selection in the Reclassify window. The screenshot shows the values you will need to enter.
If you are looking for an easy way to change specific pixels to NoData (Nan) or -9999 please take a look at this alternative script I wrote:
# -*- coding: utf-8 -*-
"""
Created on Wed Aug 12 21:33:20 2015
@author: rutgerhofste
This script will replace values in a raster and save the result in geotiff format
"""
from osgeo import gdal
import numpy as np
firstrun = 1
def readFile(filename):
filehandle = gdal.Open(filename)
band1 = filehandle.GetRasterBand(1)
geotransform = filehandle.GetGeoTransform()
geoproj = filehandle.GetProjection()
Z = band1.ReadAsArray()
xsize = filehandle.RasterXSize
ysize = filehandle.RasterYSize
return xsize,ysize,geotransform,geoproj,Z
def writeFile(filename,geotransform,geoprojection,data):
(x,y) = data.shape
format = "GTiff"
driver = gdal.GetDriverByName(format)
# you can change the dataformat but be sure to be able to store negative values including -9999
dst_datatype = gdal.GDT_Float32
dst_ds = driver.Create(filename,y,x,1,dst_datatype)
dst_ds.GetRasterBand(1).WriteArray(data)
dst_ds.SetGeoTransform(geotransform)
dst_ds.SetProjection(geoprojection)
dst_ds.GetRasterBand(1).SetNoDataValue(-9999)
return 1
pathname = "/yourpathhere/filename.tif"
writefilename = "/youroutputpathhere/filename.tif"
if firstrun == 1 :
[xsize,ysize,geotransform,geoproj,Z] = readFile(pathname)
# Set large negative values to -9999
Z[Z<-9999]= -9999
# Choose your preference: (comment either rule)
Z[Z==-9999]= np.nan
# Or
Z[np.isnan(Z)]= -9999
writeFile(writefilename,geotransform,geoproj,Z)
# Open your file in QGIS and set Nodata value if necessary for colormaps etc.
The current output datatype is set to float32.
Best Answer
You could use the Raster Calculator to do this. Square the pixel values to ensure all values are positive, and then extract the square roots to get back original number. Something like this: