TransDEM Forum

NEDF Portal: SRTM-derived 1 arc sec DEM

Geoscience Australia operates the National Elevation Data Framework Portal (NEDF):
http://nedf.ga.gov.au/geoportal/catalog ... earch.page

The 1 arc sec SRTM-based products come in three variants: Regular, smoothed ("S") and hydrologically smoothed ("H"). I recommend type "Smoothed" ("s").

See here for a visual comparison: http://forum.transdem.de/viewtopic.php?f=2&t=213.

Data is free to download for packages up to 400MB (zipped).

How to obtain the NEDF DEMs:

1. Visit the NEDF Portal search page.
2. Zoom and pan the map on the left and select your region of interest. Remember that you can only download up to 400MB in one order, therefore keep your selected region relatively small. The selection with its lat/long boundaries should appear on the right.
3. As the only other option on the right select Surface Type "DEM"
   
4. At the top right, click Search.
5. On the results page, look for "1sSRTM 2008 DEMs ESRI GRID 1sx1s Mosaic". Resolution should be 30 (metres) and Type "DEMs". The Order check-box should be enabled.
   
6. Select the order checkbox and click "Order" (at the bottom).
7. On the order confirmation page make sure the order is below 400 MB. Read and accept the disclaimer and click on "Perform order"
   
8. On the next page, enter your name and email address and continue, clicking "Proceed with order".
9. Once the order is completed, you will receive a couple of emails. At the time of writing, these are four per order. The first two ones should appear fairly quickly. The first one is simple confirmation "NEDF Portal - Order has been received.". The second one claims to request signing a form: "NEDF Licence Form(s) need to be completed." which you should check for its attachment. This attachment should contain a Creative Commons licence which you don't have to sign. After these two you have to wait for a human to check your order. Normal working hours apply, hence no service during weekends, holidays or festive seasons. Finally the third and fourth email should arrive: "NEDF Data is now being processed.". The last one, "NEDF Data is now available." is the important one:
   
   Download the data and unzip, using the password from the mail.
10. Launch TransDEM. Click the "Open DEM" function. Navigate to the location where you unpacked the NEDF data. There will be subdirectories similar to "1sSRTM_2008_DEMs_ESRI_GRID_1sx1s"_Mosaic and below "dems1sv1_0". In this last one, you will find a couple of .adf files. Select any of them. TransDEM will automatically process all other files needed.
11. After reading the data, TransDEM will open a dialog to enter DEM grid width for UTM projection. Make sure it's 30m for 1 arc sec data.
12. TransDEM will re-project the data to UTM and display the result, shown here with smoothing and shading switched on.
    

Many thanks for that, I have registered a while ago but was not sure what to select.
Do not need for Trainz purpose but for a local Historical Group use.

G'day geophil,

How did you get this to work, Roland? Twice now, I have downloaded two files (separate 'selections' from the same location) and on both occasions, despite following your instructions to the letter, I have been unable to extract the downloaded file. Every attempt to extract the files results in Winzip having fits or producing files that are unusable...

Jerker {:)}

Garry,

your download seems complete and intact and size is right? Your zip tool accepts the password provided? But extraction fails and the folder structure with "1sSRTM_2008_DEMs_ESRI_GRID_1sx1s", "dems1sv1_0" and .adf files does not materialize?

Most often the cause is a corrupt zip file despite it appearing correct.

G'day geophil,

Roland, the downloads seemed to go 'as intended' and a suitably sized file was the end result (the last attempt being of some 35 Mbytes). The problems appeared to depend upon and were different for, whichever method I used to extract them from Winzip. The ability to 'open' the zipped file in Windows achieved the 'desired' result - I was able to browse through the various folders and files and they all appeared to be there but attempts to extract them from the zipped file and/or copy them across from the 'open' folder failed. As a 'last ditch' attempt, I downloaded the file from NEDF and downloaded and installed the latest Winzip. I can't say which may have solved the problem (since both actions were concurrent) but I now have things working the way they should - except for one small detail...

...I'm sure I selected the correct area to download but when I tried to 'merge' the existing Raster Maps for the route with the new DEM, I was offered the opportunity to transform them because TransDEM detected that they were not in the same Zone (zone 55 for the DEM and zone 56 for the Maps). I thought this was 'odd' but I let TransDEM do it's thing and finished up with the DEM being almost at the top of the TransDEM display window with the Raster Maps way down at the bottom. Clearly something was amiss (I suspect my selection of the area for the DEM) but I shall try again tomorrow to see if I did something wrong in that regard...

..once again, Roland, thank you for your assistance...

Jerker{:)}

G'day geophil,

...further to my issues above, it turns out the second of my 'selections' was for a totally different area (which explains the display produced by TransDEM), so it appears that all is well, except that now I have another problem (for which, because of it's completely different nature, I shall start a new Topic, elsewhere)...

Jerker {:)}

G'day geophil,

Despite the indications above, I am still having major problems with the downloads I am receiving from the NEDF Portal. Would you be ever so kind, when you have a spare moment or two to download the file from this link...

http://nedf.ga.gov.au/download/13657319 ... 931084.zip

...and using the password "l3hgldnx1ef", see if you can do anything with it. This (and all previous attempts, except the ones that I mentioned that worked above) have failed at the unzip stage (in exactly the same way)...

Jerker {:)}

Looks all right to me:

G'day geophil,

Thank you, Roland. Indeed, I cannot argue with your result. The question that now needs to be answered is why am I not achieving this, as well? The Winzip Trial version that I downloaded and installed above has long since 'overstayed it's welcome' so I am only able to use Winrar or the built in Windows unzipper, neither of which appear to be able to unzip the file. Winrar reports errors as it attempts to extract each file using the 'normal' process...



...and as I mentioned earlier, although the Windows unzipper appears to do its thing (complete with a request for the password), the subsequently unzipped files send TransDEM off into 'crash heaven'...



...I simply do not understand where I am (or what is) going wrong, here...

Jerker {:)}

That looks like an incomplete or corrupt zip file to me. Do you have the full 80.8 MB? The NEDF server can be slow at times. My download took more than 20 minutes last night.

I am using 7-Zip on my computers. It's free, powerful and reliable. It reports alls sorts of errors for corrupt packages.

This is what you should get in Windows Explorer after unpacking ("Details" view):