[GRASS-user] Re: grass-user Digest, Vol 46, Issue 35

[Michael Barton]

On Feb 12, 2010, at 6:29 PM, grass-user-request at lists.osgeo.org wrote:

> Date: Fri, 12 Feb 2010 09:52:54 -0800 (PST)
> From: Rich Shepard <rshepard at appl-ecosys.com>
> Subject: [GRASS-user] Two General Questions
> To: grass-users at lists.osgeo.org
> Message-ID: <alpine.LNX.2.00.1002120944470.5184 at salmo.appl-ecosys.com>
> Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII
> 
>   1) Can GRASS work with TINs for elevation determinations? I've not seen
> anything about it, yet I've read that it has advantages over raster-based
> DEMs for some purposes and wonder if there are any plans to accommodate this
> data structure.

TIN's are a way of creating an elevation surface using vector polygons rather than rasters. When computers had slow processors, primitive displays, limited RAM, and limited disk space, they were a way of getting elevation in a way that optimized hardware limitations. They did so at a cost of resolution and simplicity of analysis/processing. They have also been used for 2.5D visualization, again to overcome hardware/software limitations.

GRASS can work with TIN's somewhat, creating them in v.delaunay and displaying them in nviz. However, it manages raster grids VERY fast and the 2.5 - 3.5D display in NVIZ is extraordinarily fast, using OpenGL. So IMHO, there is not much point to the hassle of TINs

> 
>   2) Is there documentation on how to drape a bit-mapped image (specifically
> from Google maps) over a shaded relief map? I know the downloaded .ps would
> need to be converted to a bit-map format using 'convert', then georectified
> with afine transformations, but it would certainly allow for impressive
> presentations when the intended audience is non-technical. For my work,
> impressive visuals is critical to accepting technical results.

This is built into the GUI. Bring up a shaded map layer and drape anything over any base map.

For display outside the GUI there is d.shaded.map  -- which is a script that calls d.his to do this.

Michael