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Zoom level not true

For discussions, questions and problems using MOBAC
freebird
Posts: 5
Joined: 08 Jun 2016, 10:32

Zoom level not true

Postby freebird » 18 Aug 2016, 14:11

Strange thing... hope you'll help.

I use local files store. These are tiles generated by GlobalMapper - geotiff exported to OSM tiles. I got directories with zooms levels 10-15 and Mobac opens it correctly - up to level 15. However zoom level 15 in Mobac looks much much smaller than size of original files (in local files directories on disc).

Have a look for comparison:
zoom15 tile (100%) from local files store:
Image

zoom15 screenshot from mobac:
Image

Is that normal? If it does, is there any other way to get higher zooms from such directory? The level 15 of zoom in local store is completely enough for me and I'd like to avoid exporting geotiff at higher level as even level 16 is painfully slow, not to mention higher levels...

Or maybe you know any other (batch preferably) method to get (many) big geotiff files to mobac?

r_x
Site Admin
Posts: 670
Joined: 25 Jun 2011, 14:00

Re: Zoom level not true

Postby r_x » 18 Aug 2016, 14:37

MOBAC displays images 1:1 regarding their size (one image pixel will be shown as one monitor pixel if the system allows it). May be the image viewer you use automatically shows small images in 400%? Or may be you have an high DPI monitor and your system scales the display of certain apps automatically?
Please read the MOBAC FAQ and MOBAC README before posting.

freebird
Posts: 5
Joined: 08 Jun 2016, 10:32

Re: Zoom level not true

Postby freebird » 18 Aug 2016, 16:04

I use IrfanView for viewing pictures and I checked if it shows 100%.

But I've just found the reason :) The difference in size was caused by the size of the exported tile. It was set to 1024x1024 pix (as on the picture above). I've changed it to 256x256 and it looks the same in Irfan and in Mobac, the same with 512x512. However, there are differences between 256 and 512pix tiles - to my surprise, although the output in mobac is identical, the export to 512pix tiles takes much longer and the jpg are about 4 times heavier.

So, 256x256pix export is the right one. Thanks for your help - somehow it was inspirational.

r_x
Site Admin
Posts: 670
Joined: 25 Jun 2011, 14:00

Re: Zoom level not true

Postby r_x » 18 Aug 2016, 16:30

The reason is simple: If you use tiles of size 256x256 MOBAC saves the tile without loading/processing it as image. It is just binary data loaded from somewhere and the saved.

If you select a different tile size MOBAC works like a image batch processor: It has to create each and every tile as image in memory which is saved at the end as image to disk. Static online map images are often heavily optimized regarding their size, MOBAC however just uses the standard image save algorithms provided by Java. You can only decrease the JPEG quality which will reduce image quality and size.
Please read the MOBAC FAQ and MOBAC README before posting.

freebird
Posts: 5
Joined: 08 Jun 2016, 10:32

Re: Zoom level not true

Postby freebird » 18 Aug 2016, 20:02

Thanks for the explanation, now it makes sense.

I can do it now properly with Global Mapper, but for some reason it won't do it in batch mode for this export format. Many other are OK, but OSM is not in favor apparently. I have about 150 files to process so I look for some more automatic way...

MapTiler would be perfect, but I'd need Pro version - and it cost a fortune.

So I'll try once more with the question if anybody knows any other (batch preferably) method to get (many) big geotiff files to mobac?

sleepybird
Posts: 35
Joined: 07 Feb 2013, 21:17

Re: Zoom level not true

Postby sleepybird » 20 Sep 2016, 09:15

You can use MapCruncher, a free tool similar to MapTiler


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