13 replies to this topic

[Anand]

Could someone please make a DEM for me from this data given. It's not that large data hope it won't take long for you people. I'm running some 2D simulation on ISIS and need to use the DEM regarding this data given. I don't have any experience on this. By the way, the data in the .txt are only the ground elevation which means Z.
Best regards

Attached Files

•  Topography_file.txt   13.29K   21 downloads

Edited by Anand, 16 February 2012 - 12:04 AM.

[frax]

You have to specify what data format the resulting DEM should be (can help if you tell us what software you will be using).

[pete.wells]

You have to specify what data format the resulting DEM should be (can help if you tell us what software you will be using).

At a guess, it looks like (s)he's using ISIS 2D (please correct me if I'm wrong). Grids would need to be in ASCII grid format with a .asc file extension.

Are the points already regularly spaced (on a grid) or sparsely spaced (requiring interpolation)?

Pete

[gregsd]

How would you go about creating the DEM? Looking at the text file, it just contains regulary spaced z-values, but there's no coordinate information or grid cell size.

Greg.

[Anand]

It is regularly spaced in both x and y axis and I'm using ISIS 2D software, grids need to be in ASCII grid format with a .asc file extension.

[Anand]

You have to specify what data format the resulting DEM should be (can help if you tell us what software you will be using).

DEM needs to be with a .asc file extension and I'm using ISIS 2D software by Halcrow.
Thank you

[pete.wells]

Hi Anand,

The file itself looks like an ASCII grid already but missing the header of the file which describes the lower-left corner coordinates, cell size etc. What software wrote the file?

If you know the cell-size and the position (x&y) of the lower-left corner of the DEM, you can write the header yourself.

Pete

[Anand]

Hi Anand,

The file itself looks like an ASCII grid already but missing the header of the file which describes the lower-left corner coordinates, cell size etc. What software wrote the file?

If you know the cell-size and the position (x&y) of the lower-left corner of the DEM, you can write the header yourself.

Pete

I'm not sure on what software it was written. Because my lecturer gave me this. I will contact him and let you know.

[Anand]

These documents might be useful to get you know about this topography.

Attached Files

•  Copy_of_Paper_by_Shao.pdf   275.59K   21 downloads
•  Copy_of_eacm163_235.pdf   234.8K   22 downloads

[Hans van der Maarel]

I'm not sure on what software it was written. Because my lecturer gave me this. I will contact him and let you know.

Eh... surely you're not asking us to do your class assignments?

[Anand]

I'm not sure on what software it was written. Because my lecturer gave me this. I will contact him and let you know.

Eh... surely you're not asking us to do your class assignments?

It's not an assignment by the way. I just need to use this topography.

[Anand]

Distance between the points are 1000m on each X,Y direction.

[pete.wells]

Distance between the points are 1000m on each X,Y direction.

OK... so we have a cell size now. This will be all you'll need to model the area in ISIS 2D, however, the results that ISIS 2D will not be properly georeferenced (as you do not know where the bottom-left corner of the grid is located).

This page: http://en.wikipedia.org/wiki/Esri_grid should show you how to write the header.

You may also need to convert the spaces between values to a single space (probably best done with a simple python script).

Bear in mind that ISIS 2D will do a nearest neighbour sampling of the DEM to populate its grid cells. This means (unless you're going to do something fancy with the data) that you'll have to use a computational cell size similar to that of your DEM (1km). If you use a smaller dx in ISIS 2D, you will end up with cells near the transitions between DEM cells with potentially large changes in z across a few computational cells which will (most likely) cause ISIS 2D to become unstable.

Hope that helps.

Kind regards,

Pete

[Anand]

Distance between the points are 1000m on each X,Y direction.

OK... so we have a cell size now. This will be all you'll need to model the area in ISIS 2D, however, the results that ISIS 2D will not be properly georeferenced (as you do not know where the bottom-left corner of the grid is located).

This page: http://en.wikipedia.org/wiki/Esri_grid should show you how to write the header.

You may also need to convert the spaces between values to a single space (probably best done with a simple python script).

Bear in mind that ISIS 2D will do a nearest neighbour sampling of the DEM to populate its grid cells. This means (unless you're going to do something fancy with the data) that you'll have to use a computational cell size similar to that of your DEM (1km). If you use a smaller dx in ISIS 2D, you will end up with cells near the transitions between DEM cells with potentially large changes in z across a few computational cells which will (most likely) cause ISIS 2D to become unstable.

Hope that helps.

Kind regards,

Pete

Cheers mate!