[OSGeo Africa] How to load .ort DEM into QGIS
Gavin Fleming
gavinjfleming at gmail.com
Tue Apr 28 01:55:36 PDT 2015
Thanks Melissa
The NGI DEM is probably a lot more accurate (and higher resolution) than
SRTM so it would be worth scripting that GRASS process if you're
concerned about accuracy.
The NGI DEM if I remember correctly is derived from stereo orthophotos,
more recent ones being done 100% digitally. SRTM on the other hand has
many artefacts. I've used this fixed-up SRTM data before:
http://www.viewfinderpanoramas.org/dem3.html.
Gavin
On 28/04/2015 08:11, Melissa Akoue Mve wrote:
> Hi Gavin and Walter,
>
> Sorry for my late response. I got caught in meetings and only managed
> to try out your suggestions late on friday and this morning.
>
> I tried both ways and they both work well. Walter's suggestion of
> downloading the SRTM 30m DEMs is the faster method because I can
> download the images as geotiffs and load them in directly without
> Grass or any other manipulation. However I have learnt a lot from
> trying Gavin's method too.
>
> Thank you both for your invaluable assistance. This discussion group
> is very valuable tool.
>
> Regards,
> Melissa
>
> 2015-04-24 13:50 GMT+02:00 Jean Paul Ngalams <jpngalams at gmail.com
> <mailto:jpngalams at gmail.com>>:
>
> Thank you Gavin for your answer to Melissa's question; I had the
> same preoccupation.
>
> On Fri, Apr 24, 2015 at 12:17 PM, Gavin Fleming <gavin at kartoza.com
> <mailto:gavin at kartoza.com>> wrote:
>
> Hi Melissa
>
> I've just done one of the NGI ort files (2631AA07.ort) in
> GRASS (result below). Pretty much everything you need is at
> http://grasswiki.osgeo.org/wiki/Import_XYZ. Note there are
> multiple spaces so you'll have to use the trick on that page
> to collapse multiple spaces to single spaces. Also note the
> coordinates are south facing TM so you'll have to do one zone
> at a time then project them together, or project all to UTM or
> Albers first.
>
>
>
> You should be able to import directly in QGIS (which uses
> GDAL) after re-ordering the data as per
> http://www.gdal.org/frmt_xyz.html. However on this one I
> tried, GDAL thinks the number of lines doesn't match the size
> of the grid it has calculated so it fails., so I just switched
> to GRASS.
>
> Good luck and let us know when you've done it (and how you did
> it).
>
> Gavin
>
>
> On 24/04/2015 11:09, Melissa Akoue Mve wrote:
>> Hi All,
>>
>> I need to do a slope analysis of the whole Western Cape
>> area. I had planned to do this with the raster tool set in
>> QGIS but after getting the DEM's from the NGI I discovered
>> their DEMs are in a .ort format which is not a standard GDal
>> format.
>>
>> I was informed that the only way to load this .ort into QGIS
>> is by converting it to a CSV and then loading the CSV file
>> into QGIS, and then converting it to raster when in DEM. I
>> have tried this but it is laborious and will take too long
>> because there are more than 50 NGI DEMs that make up the
>> Western Cape area.
>>
>> Does anyone know of a simpler way to load the .ort file. I
>> have searched for ways to convert the .ort to a geotiff but I
>> havent been successful yet,
>>
>> Kind Regards,
>> Melissa Akoue Mve,
>>
>>
>>
>>
>>
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>
> --
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