Hi Dugald, As ECW files do not store a null cell value, the compressor effectively sets the input algorithm's null cells to the input algorithm's background colour value(by default this is zero(black)) in the resultant ECW file. Assuming the background colour of your algorithm is black(check background colour in File -> Page Setup...), the majority of values outside the neat line in the resultant ECW file will be zero. However, as a side-effect of the ECW compression process, there will be a small zone outside the neatline where values will be slightly greater than zero. So carrying a null-cell value of zero across to your ECW's .ers header file will not null out all cells outside your neat line.
To ensure data outside your input file's neat line is nulled out in the resultant ECW file, you will need to copy the neat line raster region from your original algorithm into your ECW's .ers header file. To do this, follow these steps: 1. Open your ECW/ERS pair in ER Mapper. 2. From the ER Mapper main menu, select "Edit -> Edit/Create Regions..." The "New Map Composition" window should appear. 3. From the "New Map Composition" window, select the file containing your neat line raster region, and select OK. The "Tools" menu will then appear. 4. From the "Tools" menu, select the "Save As" icon. The "Map Composition Save As" window will appear. 5. From the "Map Composition Save As" window, select your ECW's .ers header file and hit OK. 6. Finally, apply the Inregion formula as you did in your original algorithm. Hope this helps. Let me know if you need anything clarified, David Carter QA Officer - ER Mapper Earth Resource Mapping Image Web Server 1.65 Released Serve TB-size images via the Internet www.EarthEtc.com -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Dugald Dunlop Sent: Friday, 1 March 2002 4:14 AM To: [EMAIL PROTECTED] Subject: Null Cells in ECW Files Hello All: I have a set of cartographic images which I would like to compress. The map tiles are bounded by Lat-Long lines and the ERS file is in UTM projection. I have therefore added the neat line as a raster region and added a formula to make everything outside the neatline polygon null. This works just fine when I view it in the algorithm, however the null cells outside the neat line are not carried through when I compress the algorithm to an ECW file. Any suggestions how I can carry the null cells through to the ECW file? Thanks Dugald ----------------------------------------------------------- To make changes to your subscription, please visit our website, http://www.ermapper.com/technicl/ermapperl/index.htm ----------------------------------------------------------- To make changes to your subscription, please visit our website, http://www.ermapper.com/technicl/ermapperl/index.htm
