TransDEM Forum

Until now, Australian Trainz routes were build either with 3 arc sec SRTM data or 1 arc sec ASTER GDEM. SRTM 3 arc sec is somewhat low on resolution, particularly in mountainous regions. ASTER, on the other hand, nominally has a higher resolution, but comes with a coarse surface. Hence, both are far from being regarded as the ultimate DEM data source.

Now, however, a gradual improvement seems on its way. It's called NEDF, National Elevation Data Framework, is operated by Geoscience Australia, and has opened its portal at http://nedf.ga.gov.au/geoportal/catalog/main/home.page sometime last year. (A TransDEM user pointed me to this address.)

They offer - for free - SRTM derived data. The derivatives are based on SRTM 1 arc sec (!), not 3 arc sec, and come in three flavours: regular, smoothed and hydrological.

Unfortunately, TransDEM 2.3.0.0 cannot yet read the data format, which is called ESRI Binary Grid, but I am working on it and achieved first results in my lab today. With a bit of luck, the task may be finished before Christmas.

Let us compare a few samples. They are taken from the Blue Mountains, NSW, west of Lithgow. The clipping is 4.5 x 3 km.


SRTM and ASTER, the familiar sources

SRTM 3 arc sec, blurry by nature.


ASTER GDEM 1 arc sec, sharper, but rather bumpy.



Introducing NEDF

NEDF 1 arc sec, regular


NEDF 1 arc sec, smoothed:


NEDF 1 arc sec, hydrologically smoothed:


In my opinion it looks best in "smoothed" flavour.

Is it accurate? One of the Open Street Map renderers has contour lines, I don't know what the source is, but our NEDF comes close.

NEDF 1 arc sec, smoothed, with OSM cycle map overlay:


To me NEDF looks like being worth a try.

G'day geophil,

Roland, please forward my 'congratulations' on to the TransDEM user who alerted you to this new 'development' in DEM technology for Australia (I was not aware of it, myself). I look forward, with bated breath (damn it, forgot to clean my teeth again, this morning), to the updates to allow us folks 'downunder' (and everyone, else, of course) to make use of this new resource...

Jerker {:)}