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Size of bgl

I

igr

Messages
113
I would like to calculate the size of bgl but I don't know how big size of the texture is in the file when I save it. Let's have instance. I have a image composed from 256x256 images. 4x3 - it was composed from 12 images of zoom 15. The jpeg file size is 169,6 kb for the file, so I calculate the size of one layer of LOD18 should be 169,6/1024/12 = 0,013802083 MB. But I think that resolution of LOD18 could take too much place. So I will convert it to LOD17 and I would like to create one big file with LODs 17 and 16 but I would like to compose it to area of dimensions of LOD 13 or 12 or 11. So here is my calculation: 0,013802083 + 0,013802083 / 4 = 0,017252604. Now multiplying to bigger area. So here I have my results: for area of dimensions of LOD13 it has onlz 4,4Mb, LOD12 area should take 17,6 Mb and LOD11 area should take 70,6 mB for layers of zoom 17 and zoom 18. If I would continue to area of LOD9 it would take more than 1.1GB. Having this number, if I would want to calculate how much would take layers of zoom 15-16 at the same dimension I just devide the number by 16. Because both layers are resized to that zooms. I continue to do it till LODs 5-6. After summery of all LODs of the same area

Conclusion:
Based on jpeg calculation I got very small number for whole area of LOD9 which is 1206 Mb (for LOD6 it is 75,3 Gb for layers 5-18). But calculation based on real size of bgl would get 16x bigger number (LOD9 should take 18,84 Gb and LOD6 should take 1205 or 1.2 Tb). So is my calculation bad or it just means that the textures in bgl file are 16x bigger then the source files in jpeg?
 
Hi,

I think starting with the jpg is the problem, since you never know how much compression the jpeg format already has. Uncompressed bgl files would be the size of a bmp/tif file when not compressed. So that is 3 bytes per pixel (or up to 5 if you add a water mask and blend mask).
 
I already know about the compression because I did some tests (not recently). I tried different compressions. The bgl which I spoke about in my post were about 75 compression (I am not sure if should I say compression or quality. To be more exact the source images were about 75 compression, but the bgl could be about 80. Not much difference in size but the difference is in the quality). I find best compression/quality 90. So there were compression in the bgl files definitely. But they could be compressed more then 80 because the source was not good quality. Nevertheless this does not explain the big difference in sizes between bgl and jpeg. Do you know what compression for textures is used in bgl?
 
Hi,

I don't know what kind of compression is used in the bgl, but in general jpg files are compressed quite a lot. My impression is that bgl files are compressed much less. So I'm not surprised you find that your jpg images are smaller.

I think most developers will never start with jpg images because of the quality. Most will start with TIF or GeoTIFF files. If possible uncompressed or with a loss less compression.
 
Hi,
using uncompressed data costs very much disk space. My graphics feeling is like that: if you want to watch streets and routes at zoom 18 or zoom 19 or even 20 you will need very good quality probably more then 90. Best should be 95 because uncompressed costs really much space. But I would be content with quality 90 for zoom 15. If I would have good source then the quality at zoom 15 will not be decreased. The quality requirements are more demanding if you really want to flight low over streets and routes because these elements often turn yellow and green colors if the source if jpeg. But how many people fly so low?

Finally I need to asked you if is it possible to use png or jpg files as source for resample.exe. I have seen only bmp using, but it does not much sense to me why developers of resample.exe decided to use bmp which is much more bigger file. Area of LOD12 in zoom 15 takes 49Mb. But the png could take about 20-250 kb approximately. Especially when you need to create blending masks or transparency masks.
 
Regarding the compression in Resample, look at its output:

Code: 
Compression statistics:

Method:  LZ1 Compressed
Blocks:  665
Ratio:   2.4 : 1

Method:  Delta And LZ1 Compressed
Blocks:  13
Ratio:   54.2 : 1

Method:  Delta And LZ2 Compressed
Blocks:  1
Ratio:   19.8 : 1

Method:  BitPack And LZ1
Blocks:  12
Ratio:   64.8 : 1

Method:  PTC
Blocks:  1784
Ratio:   2.1 : 1

Totals:
Blocks: 2475
Ratio:  2.2 : 1
 
Golf-HotelDelta, can you give me reference to the information sent by you? I have no idea what these numbers mean. Are they extracted from your scenery? If yes, what does beam the blocks items and where can I find some desciption what these methods mean?
 
igr said:
Nevertheless this does not explain the big difference in sizes between bgl and jpeg. Do you know what compression for textures is used in bgl?
Click to expand...

There probably is some loose correlation between jpeg compression and the filesize of a photoreal .bgl, but you have to remember that the .bgl contains several different variations of the photoreal sampled at various LOD levels. I'm looking at one of mine resampled from 30cm imagery in TMFViewer, the highest LOD is 17 and the lowest is 6 so if your .jpg was 30cm make a copy of it at 50% and save it in the folder alongside the original, call it "LOD16". Make a copy of "LOD16" at 50% and save it as "LOD15", etc. etc. until you get to LOD6. Check the collective file size of all the resized .jpgs including the original and I'll bet it comes close to the size of the photoreal .bgl.
 
JRobinson:
Sorry, but it's not clear to me how you save the file jpg. How is it possible to save the file from bgl file in tmf viewer?
 
Saving the jpgs as I described was only intended to illustrate why the file size of the .bgl might not correspond with the file size of your source imagery. It doesn't because the .bgl contains multiple copies of the photoreal at varying resolutions. You said your source was a .jpg. Saving the jpgs at various resolutions and adding up the collective file sizes would be a hypothetical exercise to hopefully simulate the varying resolutions of the photoreal within the .bgl, I was using it as a comparison to possibly explain the file size difference between your jpg source and the output .bgl. You don't need to actually save any jpgs and doing so would have nothing to do with the actual scenery development process.
 
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