Relative calibration exercise with raw (DN) images

From Open Foris Wiki

Jump to: navigation, search

Here is an exercise on doing relative calibration using the oft-gapfill tool with raw (DN) imagery. You can download data for teis exercise from File:Data RC.

Goals: *Create a mask using your own shapefile, practising the generic tool gdal_rasterize [1] and tool oft-calc *Practise use of tool oft-gapfill to compute linear models between image bands of the two images, input and reference

In this exercise we assume that:

  • The images are ready-made composites and have exactly the same number of rows and columns
  • The images and the shapefile are in the same projection
  • There are no clouds or cloud shadows or missing lines (L7) in the target area
  • You know how to create a shapefile in Qgis and digitize polygons

To go through this exercise, please follow the following steps:

  1. Take 2 Landsat images from same path/row from different dates (may be different years).
  2. Create a 14-band stack of your images with oft-stack:
     oft-stack 14bandimage.img reference.img input.img 
    Note that oft-stack assumes that the images are exactly of the same size. You can also extract bands and then use as in the Gap filling exercise with raw (DN) images!
  3. The calibration is based on visually selected undisturbed areas, i.e. areas that have not changed between the image dates. Manually digitize a set of these areas into a new shapefile. Give value 2 for the polygons.
  4. Create a mask for your image pair:
    • Create an empty image of the filler image with value 3, to burn your shapes on: oft-calc -ot Byte input.img mask.img
      #1 40000 ! 0 3 ?
    • Burn your shapes into the empty image:
      gdal_rasterize -a unchanged_fieldname -l shapefile shapefile.shp mask.img 
  5. Use program oft-gapfill to calibrate the values in the input image to values in the reference image:
     oft-gapfill -la 1 -nolocal -sd 5 -da -um mask.img 14bandimage.img calibrated.img 

Back to Open Foris Toolkit Main Page

Back to Tools & Exercises

Personal tools