11-24-2017 07:55 PM
I have single band 8 bit color thematic .img files loaded into Apollo Core
.img files are single layer, color thematic, unsigned 8-bit, 512x512 block, RLE encoded. 7877x7737 pixels (varies per output scale)
Note: I have also trialled equiv GeoTif with LZW compression. interestingly .img with RLE resulted in smaller files with this specific dataset - normally reverse would be true. Brief testing indicates performance of .img vs .tif similar - testing to brief to be conclusive, but likely only 2-3% difference.
Have been unable to generate good JPEG 2000 output - source data does not seem well suited for that sort of thematic mosaic (I either end up with greyscale or 3 band rgb with changed colour table). Not sure if switching to lossless JPEG 2000 for thematic would help performance.
I'm currently thinking of playing around with the 'ThematicImageChainProvider' but not sure if there would be any gains to be made.
I may be at near optimum already - just interested to see if there should be any areas I should concentrate on.
Example .img file used at 1:1066 attached.
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11-24-2017 02:12 AM
The reasons why it is not fast enough are:
Have you investigated the possibility of creating ECW mosaics (one per scale)?
I have tested your image, and with a target compression ratio of 5, at 1:1 screen scale, I cannot see the difference. But the ecw is 2x bigger in size (5MB vs 10MB) because it is a 3 bands image.
I know that it will be a huge mosaic for the biggest scale (787700x773700) but that still feasible (I know a customer with a 5x larger one).
Doing that, you will increase the reading speed and skip the virtual mosaic process. You will just lose disk space.
Just be careful with the 0 value but GeoCompressor is able to compress an thematic img into an 3 bands ECW without any problem.
Maybe you can try at a reasonable scale and see it improves performances for that scale.
11-25-2017 09:44 PM
Unfortunetly when ever I try to mosaic multiple single band 8bit thematic I get a mixed up color table
From the imagine forums I understand mosaicing an 8bit thematic is problematic. I'll start exploring converting them to 3band RGB first and see what happens.
(I should have supplied you a small set of sample .img insead of just one).
Also - I assume GeoCompressor still requires a seperate subscription license. Customer already has Apollo Pro and Imagine Pro so while GeoCompressor would be great in this sort of scenario, I don't see them coughing up for another license - will keep playing around with MosaicPro
11-27-2017 12:27 AM
Do you have a 2nd adjacent image so I can try with GeoCompressor?
GeoCompressor can be used with an APOLLO license (on the same server) for testing purpose (you get access to GeoCompressor Professional with all APOLLO licenses). See (page 22): http://www.hexagongeospatial.com/technical-documents/geocompressor-user-guide
11-28-2017 06:26 PM
Thanks for the info on GeoCompressor - definitely going to check that out - particularly as it seems to support partial area update of ECW v3 files which would be very useful. Not sure if Imagine MosaicPro does that.
I've attached sample tiles I'm compressing.
The PNG folder has the original source PNG files plus Aux added defining the map projection.
Currently I then convert PNG to IMG files. Sample single band IMG files also included.
Currently I have to use Imagine to convert from PNG to IMG, so its an easy change to go from PNG to 3 band IMG (already done) - so don't worry if you can't go from IMG (single band) to a mosaic.
Now, if it were possible to directly mosaic the PNG files to ecw that would be something, though I doubt that would work.
11-28-2017 07:28 AM
It works fine with GeoCompressor (I just set "0" as null value, it took 17s with my laptop). I chose a target compression ratio of 5, the output is 30MB but maybe you can try to use a higher ratio.
01-19-2018 11:28 PM
Do you have Pyramid files?
If you don't have them you can generate them with Imagine and drop them into the same folder as the image, then Apollo Core will use them.
This makes a big improvement to performance.
01-22-2018 04:54 PM
I didn't generate pyramid files.
I ended up generating JPG files instead of PNG and found GeoCompressor directly reads them. So currently using .jpg -> Geocompressor -> ECW. Still working through client testing phases but looks very promising. Yet to muck around with tranparant images, lower priority. Client likes that in Apollo Core they can also create a derived product by overlaying the thematic basemap over aerials (with transparancy applied using Image Chain ) saving a lot of generation / mosaicing processing time.