From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 22082 invoked by alias); 22 Sep 2004 02:59:37 -0000 Mailing-List: contact xconq7-help@sources.redhat.com; run by ezmlm Precedence: bulk List-Subscribe: List-Archive: List-Post: List-Help: , Sender: xconq7-owner@sources.redhat.com Received: (qmail 22074 invoked from network); 22 Sep 2004 02:59:36 -0000 Received: from unknown (HELO urk.execulink.net) (199.166.6.45) by sourceware.org with SMTP; 22 Sep 2004 02:59:36 -0000 Received: from diamond.ansuz.sooke.bc.ca (ppp288.ac2.56k.execulink.com [209.239.26.34]) by urk.execulink.net (8.11.6/8.11.6) with ESMTP id i8M2xY326403; Tue, 21 Sep 2004 22:59:34 -0400 Received: from localhost (mskala@localhost) by diamond.ansuz.sooke.bc.ca (8.10.2/8.10.2) with ESMTP id i8M2tbe29533; Tue, 21 Sep 2004 22:55:37 -0400 Date: Wed, 22 Sep 2004 16:36:00 -0000 From: mskala@ansuz.sooke.bc.ca To: "D. Cooper Stevenson" cc: Xconq Mailing List Subject: Re: GIS Update In-Reply-To: <1095818641.27063.71.camel@localhost> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-SW-Source: 2004/txt/msg01217.txt.bz2 On Tue, 21 Sep 2004, D. Cooper Stevenson wrote: > 1) We are not after satellite photos, we are after "Digital Elevation > Models." Well, depending on what you want to do with it. A DEM is a height field. It specifies the elevation at a bunch of points. If you are building a map that cares about elevation, then you want that for sure, but you might want other kinds of data too. For my Antarctic map I also used the DEM to infer the surface type, because that seemed the most useful thing to do, but that was something of a kludge adapted specifically for the Antarctic map. On other maps there are probably other kinds of data that can provide better guidance as to the final "bin" to put the hex in. For instance, if we had multispectral data (like from a LANDSAT TM image) we could use that to classify hexes by type of surface terrain - forest, cropland, water, etc. That could be useful. LANDSAT TM is like an image file with five or six channels of colour information (corresponding to colour bands from visible into infrared, with some subtleties and complications) at a resolution where each pixel is 15 to 25 metres. I don't know that we could get that for free, but I'm pretty sure we can get AVHRR data (similar kind of thing, pixels are kilometres in size) for free. If we had "line coverages" of vector data for things like rivers, it might be fun to try to convert those into border or connection terrain, although the complexity of the algorithms to do that might get pretty high. Part of the fun is that there are lots of different kinds of GIS data out there. > 2) Because the data is in a raster format (as apposed to a regular > image file), I believe it is quite possible to automate the creation of > new maps and smaller scale views of those maps One thing to watch out for is that not all DEMs are really rasters. Some are just lists of points; others are complicated data structures called Triangulated Irregular Networks or TINs, and even if they are rasters, they may not be on the grid or projection you want. GRASS has some pretty sophisticated tools for manipulating the data into whatever grid you want, so that shouldn't be a problem, but it'll be something to keep in mind. -- Matthew Skala mskala@ansuz.sooke.bc.ca Embrace and defend. http://ansuz.sooke.bc.ca/