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Elevation analysis includes "No Data" value?

Started by Elena V, February 07, 2013, 09:17:06 PM

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Elena V

Hi again,
I'm using SLAMM version 6.2 (which has some really neat new features!). I just ran an elevation analysis on the same input data as I was using in version 6.1 and it looks like the value corresponding to "no data" (-9999 in this case) might now be included in the elevation analysis. This mainly shows up in the results for the dry land categories (the mean elevation is ~ -6000 m NAVD) since these areas are at the edges of my study area where I don't have topo data.

Just wanted to confirm that this is what's happening because I want to be aware of any skew it might be introducing to the other veg categories (where there are fewer "no data" points so it might not be as obvious).
Thanks!
Elena

marco.propato

Hi Elena,
the latest 64bit version should have fixed this problem and exclude the nodata elevations from the statistics. It is a possibility: are you sure that in the elevation raster, the no data elevation is set to -9999? That should be written in one of the first lines of the raster file. You can open it with notepad (if it is not too big) or notepad++ or preview it if you change the file extension to txt. Otherwise you can send me an email if you still observe the problem.

Hope this helps



 


Elena V

Thanks for the response -- I did install the latest 64-bit version of v6.2 and checked that the no data elevation is equal to -9999. I used the exact same inputs in v6.1 and v6.2, but in v6.2 the statistics are slightly different for all habitat types, and the statistics for dry land categories includes -9999 in the statistics. This did not appear to be a problem in v6.1.

Elena V

I just ran the elevation analysis again and it seems that this is only a problem when using NAVD88 as the "Zero". This does not seem to be a problem when I use MLLW, MHW, MTL as the Zero.

marco.propato

Thanks Elena,
I will have a look at the code on what is happening by selecting the different zeros. In the meantime, if you want to try, you could change all the no data values from -9999 to 999 and that may solve it for now. I will get back to you next week.


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