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| By How Much Should I Reduce a Large Bitmap Raster Image? https://forum.transdem.de/viewtopic.php?f=7&t=480 |
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| Author: | Plantagenet [ 30 Jan 2017 13:53 ] |
| Post subject: | By How Much Should I Reduce a Large Bitmap Raster Image? |
I’m working with Ordnance Survey Open Maps District for the raster files. Could someone please tell me how much I should reduce the images by when the ‘This bitmap is rather large’ dialogue appears? The OS District maps are 16Mp in size and my route will require eight of them I’m also curious as to what the advantages/disadvantages are between large and small raster bitmaps. I’m very new to TransDEM and hope that I’ve phrased my question correctly. Any help would be greatly appreciated. Peter. |
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| Author: | Jerker [ 31 Jan 2017 02:33 ] |
| Post subject: | Re: By How Much Should I Reduce a Large Bitmap Raster Image? |
G'day Plantagenet, Peter, you may have discovered, already, that there is no compunction on your part to reduce the size of any 'large' raster file (so designated by that particular warning message), should you not desire to do so (the warning will not prevent TransDEM from performing the required 'processing' upon it, provided that your system can handle it). I regularly "ignore" that message but if it does prove to become an issue, then I will undertake a 50% reduction (using the built-in TransDEM 'function'). Bear in mind that this will affect the quality of the image, minimally, mind you, compared to the 'drastic' effect that the 'lack of resolution' Trainz 'applies' to it, has, once it is exported but it is noticeable... ...by the way, I like your "moniker"! Do you actually have any 'genuine' claim to that 'surname'?? Jerker {:)} |
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| Author: | Plantagenet [ 31 Jan 2017 10:30 ] |
| Post subject: | Re: By How Much Should I Reduce a Large Bitmap Raster Image? |
Hello Jerker, Many thanks for your prompt and full response to my question. That's another hurdle safely stumbled over. As for my user-name, no I only have the basest peasant blood flowing through my veins but after reading Shakespeare's Richard III in school, and learning what a villain he was, I've always been a big fan. Thanks for your help. Plantagenet. |
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| Author: | geophil [ 02 Feb 2017 09:41 ] |
| Post subject: | Re: By How Much Should I Reduce a Large Bitmap Raster Image? |
Technical background: Some of the bitmap processing algorithms in TransDEM use lossless 64 bit integer arithmetic. As long as the two operands stay in the 32 bit address range, everything is fine. If not, the operation result may exceed the 64 bit address range under specific circumstances, ending with an exception. "Rather large" gives an indication that this might happen. It usually won't, and, as Garry says, you can normally ignore the warning. Only if it fails, you will need to further reduce size and/or resolution. |
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| Author: | Plantagenet [ 04 Feb 2017 09:24 ] |
| Post subject: | Re: By How Much Should I Reduce a Large Bitmap Raster Image? |
Thank-you both for your help. Plantagenet. |
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