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Recommended system requirements for processing large DEMs


Ahmadi
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Hi,

We want to process large area Digital Elevation Model (greater than 2 million square kilometer SRTM 3 DEM with ~90 meter pixel size), we are thinking to use one of DEM processing software (WMS or RiverTools) and we would like to know the capability of WMS to process large DEMs. Also I have some related questions for example:

Does WMS support 64-bit operating systems (i.e. Microsoft Windows XP or vista)?

Do you think using 64-bit operating system will be useful for us if we want to use WMS?

Does WMS support some advanced techniques like multi-threading, multi-tasking, multi-core processors, and multi processors?

Do you think these techniques helpful for us if we want to run WMS with large DEMs?

Thanks

Ahmadi

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Does WMS support 64-bit operating systems (i.e. Microsoft Windows XP or vista)?

WMS does not support 64-bit operating systems. It will work on those systems, but it will run in 32-bit mode.

Do you think using 64-bit operating system will be useful for us if we want to use WMS?

No, because there will be no difference in running WMS on a 64-bit system and on a 32-bit system.

Does WMS support some advanced techniques like multi-threading, multi-tasking, multi-core processors, and multi processors?

Only to the extent that these are supported by the operating system. WMS itself will not make use of multi-core processors. It will only use a single processor.

Do you think these techniques helpful for us if we want to run WMS with large DEMs?

Yes, these techniques would be helpful, but they are not supported. Besides processing limitations, you will run into a RAM limitation if you try to read this size of a DEM. WMS stores all its data in the computer's RAM. According to my calculations, if you try to read a 2 million square km DEM into WMS at a 90 m pixel size, and each DEM cell requires 16 bytes with attributes, you will use over 3.5 GB of RAM trying to read this DEM. Since the maximum practical amount of memory support on 32-bit Windows systems is about 3 GB, it would not be feasible to try to read this much data into WMS.

One feature that WMS has is a DEM thinning factor. This factor is useful if you're trying to model a large area. Instead of reading every single point, WMS will read every 2nd or 3rd point, and your DEM will require much less memory. Usually, thinning the DEM would be the best approach instead of trying to feed a large DEM into WMS in hopes of getting a more accurate result.

The question you have to ask yourself is whether the hydrologic model is accurate enough to require a high resolution DEM and an exact delineation of all your sub-basins. The answer is usually no, because the kind of data hydrologists need to model an area with this kind of accuracy just does not exist.

That said, I think WMS will support 64-bit computers with faster processors and more memory sometime in the near future. We may even support some limited multi-core processing capabilities.

Chris

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