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I just received a batch of imagery for my project area in 2 formats: Geotiff (RGBI) and ECW. The imagery looks very similar and covers the same footprint, but the file size difference is massive: 270GB for the Geotiffs vs 11GB for the ECW.

Is there any added value in the RGBI Geotiffs I should be aware of? Is it even worth taking up this kind of server space to store this data?

The intended uses include map making, landscape change monitoring, visualization, and supporting engineering work... but always looking for new & interesting ways to make use of the information we have.

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1 Answer 1

As is evident from your file sizes, the ECW files are compressed while Geotiffs do not seem to be (though, I believe geotiffs support compression). If you are only using the images as a background on maps, I recommend using the ECW because of their size.

As you mentioned, since you are using them for change detection there may be artifacts in the compressed files which may affect your image classification results. My understanding of RGBI is that they contain information which may aid in your landscape change monitoring.

I recommend storing both formats.

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GeoTIFF can be compressed. One of the disadvantages and important things to remember when working with ECW is the license required by ERDAS/Intergraph. Both GeoTIFF and ECW can contain multiple bands and thus they both can include the near infrared (NIR) colour channel. –  Chau Sep 4 '12 at 7:00
    
Thanks Fezter. Does anyone have any specific information on the I band in RGBI - how is it useful? This is really what I need to know to decide whether it's worth taking up 270GB on the server. –  John Bryant Sep 4 '12 at 10:19
    
The I-Band refers to the NearInfraRed (NIR) channel. When you rotate your RGB visualization of the channels corresponding to R=4, G=1, B=2 you get a False color image showing you the condition of vegetation. In simple words: Healthy vegetation emits NIR and shows up in Red in your image. –  Jürgen Zornig Jun 10 '13 at 11:51

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