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gtopo30 export to arcascii

rcman
rcman Global Mapper User
edited May 2010 in Elevation Data
Hello,

I am loading in a GTOP030 file (W180S60.DEM), which I previously uncompressed with Izarc, into Global Mapper 11.02 (64bit) and then I am exporting it to arc ascii grid.

The last row of data in the arcascii file is all -9999 values....which should not be there.

What have I done wrong here?!

Source data:

http://eros.usgs.gov/#/Find_Data/Products_and_Data_Available/gtopo30/w180s60

Thanks.

Comments

  • Frank2
    Frank2 Super Moderator
    edited May 2010
    I seem to recall that the GTOPO data doesn't have complete coverage to the poles, but it's been many years since I used that data.

    Examining the raw DEM file though, it does have -9999 values at the end, so you're not doing anything wrong.
  • rcman
    rcman Global Mapper User
    edited May 2010
    Thanks for the reply.

    GTOPO30 does go to the poles. You may be thinking about the SRTM30 as data which I believe is not global.

    Can I ask you a favour. You were able to interogate the W180S60.DEM file and note that it does have a last row of -9999 values. Could you also confirm that this file also has a first column of -9999 values.

    Any ideas why this might be?

    Thanks again.
  • Frank2
    Frank2 Super Moderator
    edited May 2010
    OK, like I said, it's been MANY years since I used that data set ;)

    Yes, the file does start with -9999 values too, but that's because ocean values are stored that way (voids).
  • Frank2
    Frank2 Super Moderator
    edited May 2010
    You could try the ETOPO1 if you want combined bathymetry & elevation data:
    http://www.ngdc.noaa.gov/mgg/global/global.html
  • rcman
    rcman Global Mapper User
    edited May 2010
    Thanks for all your replies.

    I was only concerned about the first/leading column and last row of that particular antarctic area. I realise that the oceans are assigned null values (in this case -9999). I was concerned as to why this file has null values for the first column and the last row. I thought it might be something that Global Mapper had introduced during import/export.

    I'll ask the USGS for comment.
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