IMPORT SATELLITE IMAGES INTO ILWIS GIS

In this brief instruction we will help you on the way on how to import a raster satellite image into ILWIS GIS.

After you downloaded your image, and extracted a ".tif" file from the compressed files. See "download satellite images"

Now, before we go any further, I recommend that you start your project in a very organized fashion, which usually starts out with receiving and downloading files and images. GIS projects may get quite messy when one works with a variety of maps and images.

Extracting the files of the satellite images

The satellite images are usually heavily compressed into .tar.gz files, which can be decompressed with " 7Zip ", a great free open source programme. These compressed files may contain a variety of file by wavelength or colour. Each of those files are quite large, so I would suggest to only extract the wavelength that you need. I prefer to work with .tif files but formats may vary by provider.

A common error when working in GIS is that many GIS specialists organize their files very poorly and as a result, important information gets losts. So I highly recommend that before downloading and receiving files, you get well-organized and make a directory system with a folder for each satellite image that you download and name them after path number, row number, year, month, day. If you do that consistently, your satellite images will be automatically organized in the directory of your project. Only a very clean and well-organized directory structure will allow you to keep track of all the files in your project. After all, it is a Geographical Information System, GIS; not a chaos.

A project directory may look like this:

ecosystems_map

                        el_salvador

                                        images

                                                            18_51_2009_11_25

                                                            19_50_2008_10_30

                                        dem

                                                            astgtm_n13w088

                                                           astgtm_n14w091

                                        vector_maps

                                                            elevation_lines

                                                            roads

                                                            hydrology

                                                            ecosystem_map

After you have extracted the image files in the appropriate directory, you are now ready to prepare them with ILWIS GIS.

Open ILWIS Click Navigator in the left window. Select the drive that contains your data; select your project directory and the folder where your satellite images has been stored. This is important, because ILWIS safes your files where you have positioned yourself in this stage. I you don't do it correctly, your files may end up somewhere else and you may have great difficulty finding your data back and letting ILWIS manage your data properly

In the general menu go to file>import:

appears the import box showing +ILWIS. Click on +

click on + of +raster

Select "Tagged Image File Format.TIF

Select Input by clicking on ...> select the tif files of your need. In the case for my most common needs in Landsat TM for Ecosystems mapping, I need the bands 4+5+3. So I only extract those, to avoid unnecessary occupation of space.

Chose an output name. To be systematic, continue with the path, row, date followed by _4, _5, _3. Check if it sends the output file to the right directory! If you go to the target directory, you will find the composed files belonging to that raster file. If the file did not got to the correct directory, DON'T move it. Re-make the file, in the correct directory and have ILWIS delete the file in the wrong directory. That way ILWIS remembers where your files are.

The next step is to prepare a colour composite:

In the Main Menu: Operations>Image Processing>Colour Composite

In new window mark 24 bit; Linear Stretching; RGB; Percentage. Then select the colour bands. The order of the images is important and varies by subject. For vegetation and ecosystems mapping we need bands 4,5,3 in that order.

In Red Band select image 4; in Green Band select image 5; in Blue band select image 3.

In output name put path, row, date, _453 or whatever combination of bands you have prepared.

In window "display options" mark info; normal, OK

This opens your composite satellite image.