I have 18GB ecw image, how to cut down to make smaller file sizes/tiles?

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06-05-2013 08:19 PM
Regular Contributor
Hi,

I have been given an 18gb ecw file from the company that flew over our city a couple of years ago, but nobody ever asked to receive this image in smaller tiles. Now i am trying to use the aerial photography on our survey equipment I am tryin to cut the image up into 500mb files.

Has anyone ever done this with GIS, and if so was it difficult? I would prefer to try do it myself as the company that flew the imagery are happy to charge us a pretty penny to do it for me.

Thanks
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Regular Contributor
This question was raised again here at work, and a solution was found here.

Just tidying up my threads and thought I would mark it as solved with the solution used.

Cheers

View solution in original post

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Regular Contributor
Is your raster 18 gigs for the uncompressed size or 18 gigs on disk?  Generally speaking, ecws are highly compressed and are much larger when it comes to uncompressed size. You can attempt the Split Raster tool, but bear in mind you will most likely be processing it a long time and it will take up a considerable amount of space.
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Regular Contributor
Is your raster 18 gigs for the uncompressed size or 18 gigs on disk?


I assume that it is uncompressed on disc at a size of 19.6gb (my original post was a guestimate, i just checked actual size).

See screenshot for files...

Thanks
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Regular Contributor III
Ben,

Go to the raster layer properties > Source tab and check the uncompressed size.  The size on disk is the compressed size.

Best,
Eric
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Regular Contributor
Hi Eric,

I now see what you are talking about, the uncompressed size is 162.59gb.

I have started a split raster command as we speak, just chopping it up into 15 x 15 tiles, ill see if they are more managable.

Is there a tool that will generate an index of all the images and corresponding file names? Save us guessing the file names when inserting the images.

Thanks
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Esri Contributor
Ben,

18GB for 1 ECW is about Right. The Entire New South Wales ECW is 45GB. The size is your problem. Unfortunately the ECW .dlls that are provided with ArcGIS Desktop do not allow you to extract from or convert ECW images over 2GB. This is a licensing restriction on the publicly available ECW sdk. However there is a work around to this. You can convert the ECW's to a tiled cache in a mosaic dataset and then export from this tiled cache. The workflow to create your tiled cache at 10.1 SP1 is as follows:
1) From ArcGIS Desktop create a new Mosaic Dataset in a file geodatabase (Create Mosaic Dataset)
2) Add the ECW�??s to the Mosaic dataset (Add rasters to Mosaic Dataset)
3) Remove the padding around the edge of the images. (Build Footprints)
4) Create the Mosaic dataset overviews (Build Overviews)
At this stage now we have a seamless mosaic of all the ECW�??s which can be consumed by ArcGIS Desktop.  The solution is to create a Tile Cache to allow extraction is as follows:
5) Build a Cache tiling Scheme (Generate Tile Cache Tiling Scheme) This tiling scheme defines the scale levels and dimensions for the different levels in the cache.
6) Build the Tile Cache. (Manage Tile Cache)
7) Create a new Mosaic Dataset in a file geodatabase. (Create Mosaic Dataset)
😎 Add the tile cache to the Mosaic Dataset (Add rasters to Mosaic Dataset)

In ArcMap now you can draw shapes and use the export data tool (right click image ->export data)to export your rasters at the desired sizes.

Hope this helps
Gordon
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Regular Contributor
Hi Gordon,

Thanks for that reply, you have just filled in my friday afternoon nicely! I'll give that a go also.

-Cheers
Ben
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Regular Contributor III
Unfortunately the ECW .dlls that are provided with ArcGIS Desktop do not allow you to extract from or convert ECW images over 2GB. This is a licensing restriction on the publicly available ECW sdk. However there is a work around to this.


There is no such restriction on ECW files in ArcGIS.  I just ran Split Raster on a 4.5GB ECW file and created 100 Tiff files totaling ~110GB of data in 3 hours of processing time.

Best,
Eric
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Esri Contributor
G'day Eric and Ben,

I will admit I have learn't something new over the past couple of days. I have been working with ECW's and ArcGIS for some time. I have encountered situations where it has been difficult to translate the ECW's to other formats and have put this down to the distributed ECW .ddl's.

Today I took a 10 GB ECW and used the split raster tool. I split this image into 2300 unique Jpeg compressed Tiff images, each 10000 x 10000 pixels. It took 8 hours and consumed an extra 88 GB of disk in the process. However, it worked with out fail and that is the important point.

So now there are two methods to break this image down. The tiled cache method recommended earlier and the split raster tool.

regards
Gordon
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Regular Contributor III
I just want to add that you can pretty much do anything you want with an .ecw file in ArcGIS.  It is fully supported by the core product.  Yes, there are restrictions on "serving" them without extra licensing, and we also do not "write" this format, but other than that you should be able to do want you want in terms of conversion/geoprocessing/etc...assuming you have enough disk space. 😄

Best,
Eric
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