TransDEM Forum

TransDEM News, Support, Hints and Resources
It is currently 28 Mar 2024 13:03

All times are UTC + 1 hour




Post new topic Reply to topic  [ 4 posts ] 
Author Message
 Post subject: USGS Files for Transdem
PostPosted: 13 Aug 2016 22:25 
Offline

Joined: 13 Aug 2016 03:08
Posts: 6
Hello,

I've visited the USGS DEM D/L site and entered the various data selections. I received a listing of files that consists of the following:

Four files were similar to "n30w095" for a file size between 121,735KB & 463,482 KB zipped, and
145 files similar to 569b47ece4b0ec0512962bbf 7.5 x 7.5 minute.gda. I would guess that the average size of the files is about 2,500,000 bytes. The smallest I spotted in the database of the saved files was 768,118 bytes and the largest 4,081,535.

My question is "Do I need to download both the 145 .gda files and the 4 larger files? Or just one or the other file type ?

Thanks,

Dave


Top
 Profile  
 
PostPosted: 14 Aug 2016 02:17 
Offline

Joined: 30 Jan 2011 13:03
Posts: 170
G'day davedingler,

...you certainly don't need to download every single one of them, Dave (if I may be so bold)! A lot will depend upon the area you need to cover and this will always determine the total number that the viewer offers for your selection. The four large files (labelled as "n30w95", for example), in your case, are the full 1 degree x 1 degree (lat/long) DEM tiles that most of us tend to use. From the four that you have, you should choose the one (or more as appropriate) that is/are suitable for your purpose (they are subtly different, depending upon how the data has been modified, which is explained in the descriptions provided). I usually choose the 1/3 arcsec, "Hydrologically Enforced" dataset but ultimately, the choice is yours. The other 145 files are 'smaller' chunks from each of these larger sets, known as "Quads". There are four of these "Quads" in each full sized tile and these cover an area of 7.5 minutes (square), each, hence their name. Sometimes, it is advantageous to grab these smaller ones as is required but I usually just get the big ones and reduce their size in TransDEM (using the provided tools) once I see how much needs to be kept/rejected to surround the map tiles that I have already imported...

Jerker {:)}


Top
 Profile  
 
PostPosted: 14 Aug 2016 04:50 
Offline

Joined: 13 Aug 2016 03:08
Posts: 6
Thanks Jerker,

I had downloaded the larger files, but hesitated on downloading the smaller ones. I have them in a CVS file so I can get back to them if needed. I'll do some research on GE to see what areas that I need to have & go from there.

Dave


Top
 Profile  
 
PostPosted: 14 Aug 2016 22:45 
Offline

Joined: 30 Jan 2011 13:03
Posts: 170
G'day davedingler,

Dave, if you have your Raster Maps open in TransDEM, you can find out exactly how many and which DEM tiles you need to cover the area of your interest from the program, itself, by clicking on the File/DEM Menu>File Name info STRM.hgt selection, which will open a dialogue box showing a list of every tile needed for you to get from your source...

Jerker {:)}


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 4 posts ] 

All times are UTC + 1 hour


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  

Imprint & Privacy

Powered by phpBB® Forum Software © phpBB Group