calculate river slope from coarse DEM

Here is one way to calculate the slope of a stream (and long profile) from a coarse DEM.

(1) If the DEM is huge, clip it to only the area of interest, to speed up the processing. You can do this by creating a polygon outlining the area, adding it to the map, and then using extract by mask (Spatial Analyst, Extraction, Extract by Mask).

(2) It may help to visualize things by making a Hillshade.

(3) Under Spatial Analyst, Hydrology, there are three steps.

(a) Fill

(b) Flow direction

(c) Flow accumulation

(4) Now you want to extract the stream by choosing an upstream point, then selecting all points with a flow accumulation greater than that value, using the conditional to turn the map to 0s and 1s to delineate the stream, and then turn that stream into a vector.

Map algebra, Single Output Map
Conditional

Hydrology
Stream to feature (may be optional and affect choice in Step 5)

(5) Select equally spaced points along this line either by using Hawth’s tools / Geospatial Modeling Environment or this previous post.

(6) Extract Values to Points, Export data

(7) You can open the .dbf in Excel or Gnumeric to inspect the slope.

There’s also this:
Tarboton, D. G., R. L. Bras, and I. Rodriguez-Iturbe. 1991. On the Extraction of Channel Networks from Digital Elevation Data. Hydrological Processes. 5: 81-100.

Clip a Raster to a polygon - GIS

Make a new polygon with the shape you want.
Toolbox:
Data Management Tools>Raster>Raster Processing>Clip
Your raster in the "input raster"
Your polygon is the Output Extent
(check the "Use Input Features for Clipping Geometry (Optional)" box)

italian insar site

This link has been stuck in my inbox for a long time, courtesy of JP. Might as well archive it here. We're all about databases.

http://webgis.irea.cnr.it/webgis.html

IREA-CNR InSAR WEB GIS

(wow. acronyms.)

matlab + geospatial

futzing around on matlab help site and ran into this:

Geospatial Data Import and Access
http://www.mathworks.com/access/helpdesk/help/toolbox/map/ref/f3-12193.html#f3-32594

which includes things like:

usgs24kdem
Read USGS 7.5-minute (30-m or 10-m) Digital Elevation Models

Really?? I guess you need Mapping Toolbox and I'm not sure if that comes standard.

more gis tools

Geospatial Modelling Environment
http://www.spatialecology.com/gme/gmecommands.htm

Yesterday Jon downloaded something from the predecessor of these tools, and the interface and functionality looked really good. You can do a bunch of stuff with points, lines, polygons, that I think is more intuitive than arcGIS.

Also, linked to that page is a whole list of open source GIS. Who knew??

Quantum GIS
GRASS GIS
uDIG GIS
SAGA GIS
OSSIM Image Processing
The R Project
PostGIS
Wikipedia GIS Page

Brain about to explode.