You might find something here: http://www.exelisvis.com/docs/home.html

Hello and thanks for the answer. I read the 'visualize Data' section but I did not find anything which is about comparison of two or more raster data sets. Am I searching the wrong section? I am really thankful for very advice and wish a nice day John

Hi John, What do you mean by "comparing" two raster data sets?. Because with IDL you could compare two arrays, looking for something specific. Like: http://www.exelisvis.com/docs/ARRAY_E... ; Return True (1) if all elements of a are equal all elements of b: IF ARRAY_EQUAL(a, b) THEN ... Or, another example: IDL> a=findgen(3,3) IDL> b=findgen(3,3)*2 IDL> print, a(where(a eq b)) 0.000000 IDL> I don't know, it will depend of what you need to do I guess. There are more Array Manipulation routines here: http://www.exelisvis.com/docs/Array_M... Cheers, fernando

Hello Fernando, first I want to thank you for your answer. Second I apologize for my bad description of what I want to do. I have two .tif images of the brasilian rain forest. One image is the land cover map (230 metres) and the other image a disturbance map (25 metres). First I am not sure how to compare two images with different resolution. I thought about to classify the disturbance map image (cause the resolution is higher) and compare to the pixel of the landcover map. If the pixel in the under lying landcover map have the same class, the pixel of the landcover map will be set to 1, if not the pixel will be set to 0. This is what I have in my head. I am not quite sure if my thoughts are correct and. And I am not sure how I can realize this with IDL and this is why I am searching the internet for a solution since many days :-) I hope now it is clearer what I want to do. And I am still very thankful for every help of you :-) Greetings John

Do you have ENVI? ENVI has Image difference tools like you describe, for both image pixel and thematic (classification) data.

MariM wrote: Do you have ENVI? ENVI has Image difference tools like you describe, for both image pixel and thematic (classification) data. No. I only worked with it during my university studies. With ENVI it is easier to solve my problem, but I don't own it, and so I have to choose the more difficult way :-)

No ideas?

Hi John, (Assuming you are using IDL 8.2.3. Try including the version(s) of IDL you are using as not all functions in the current version are available in previous versions) For starters you will need to at least open the images you have.You can use the IMAGE function to do this. If the images have a projection you will need to use other functions which are demonstrated in the IDL Help under: Graphics > Graphics Gallery> Maps > Map Image. To resize your images you can look at implementing one or both of the following on either one of your images or both: CONGRID and REBIN. You may be able to overlay one image over top of the other depending on what functions you use. Check for relevant /OVERPLOT keyword. To find particular pixel values or ranges of interest you can use the WHERE function. There may be other functions that you can use depending on what you need for processing steps.