gtopo30 export to arcascii

rcman

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.

Frank2

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

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

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

You could try the ETOPO1 if you want combined bathymetry & elevation data:
http://www.ngdc.noaa.gov/mgg/global/global.html

rcman

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.