Thomas Adams wrote: > > I work for the US National Weather Service at the Ohio River > > Forecast Center. We generate, on a daily basis, a graphic that > > looks like this: > > http://www.erh.noaa.gov/er/ohrfc/fop.html
the site seems unreachable today for me.. endless wait. > > The linked graphic would be pretty trivial to create in GRASS using > > ps.map. However, during times where there is a reasonable risk for > > significant flooding, the map must be altered to designate the > > smaller subbasins (or areas) that are at risk and to annotate the > > period over > > which the threat exists. I'm sorry I can not link an example to > > show, since there is no current flooding in the US or risk thereof. it is simple to script ps.map with variable text & queries. see example script below. > > Currently, the process is carried out interactively using ArcGIS. > > I am trying to offer up an open source alternative with GRASS. I > > am sure a > > more sensible, non-interactive way of generating the map explicitly > > through a modeling approach would be best (and we do, of course, > > base designating the basins at risk on hydrologic modeling), but > > there is no *direct* link. Currently human interaction is used and > > some will insist on this. Human interaction is fine, at times of public risk human oversight is critical. Automation is a great help though, and if the digitizing work can be 95% prepared for the operator - and they just have to touch it up - then all the better for speed of deployment & reduction of opportunities for human error. > > So, I am left wondering how to best approach this is GRASS, > > namely, either: > > > > (1) have the ability to manually select smaller subbasins and > > group them together to designate the area at risk, or see script below for generating map simply from specified catchment IDs. > > (2) hand draw/digitize the area Digitize areas with v.digit over backdrop image. Backdrop image can be static or with raster overlay from hydrologic model output. (or digitize with QGIS, or digitizing frontend like OpenLayers WPS- try the polygon tool: http://www.les-ejk.cz/english/pywps-and-openlayers ) [...] > Sorry for not being clear. Basically now the mode of operation is: > > (1) launch ArcGIS which has been customized somewhat to do the following > (some background coverages appear automatically for reference, as the link > shows)... > (2) the user manually digitizes polygonal areas corresponding to the areas of > flood risk this seems highly inefficient to me. > (3) the polygons are annotated to show the period over which they are valid > (4) the custom control buttons allow the user to export the map and to have a > text file created and have it ftp'ed to another location > > Now, all of this is pretty much doable in GRASS, though the GUI is not as > refined and some coding changes would be needed (I think) to 'duplicate' this > process. It seems best done from a script, in which case the GUI is moot and the CLI is king. If partial interaction is required, the script could be written to pop up the digitizing tool as needed, then preview, "Accept or Re-edit", and finally continue the script to do the rest. A g.parser script could be made friendly & have checkboxes (e.g. the v.clean GUI tool selection) to activate catchment by names/ID. Or a fancy front end could allow the user to click on an area of a map. (e.g. parse 'd.what.vect -xft'; or generate from the HTMLMAP monitor driver [see d.mon]; or pyWPS style solution) > I'm trying to avoid this right now for several reasons, including > time constraints. What I thought *could* be done, would be to have some > reference subbasin boundaries displayed in the GRASS display window along > with the other reference vector maps (state political boundaries and our area > of responsibility). Allow the user to interactively select the basins at risk > and have those areas ONLY display as areas of risk. hopefully the model output will tell you (ie the script) which subbasins are at risk... > Then the process would be similar to (1)(4), except that: > > (1) I do not see how polygons can be manually selected and have the option to > remove unselected basins/polygons and limit by known catchment ID (vector feature category) or SQL query on vector area attribute (catchment's name). Make the query part of the script set by a environment variable, see example below. > (2) I do not see how to manually annotate a polygon in such a way that the > polygon(s) are clearly tied to the annotation. In ps.map there is the vlegend instruction which does this automatically. d.legend will display raster category labels, if present, and hide cat numbers. > However, this may all be moot because, it seems, a significant number of > people want to have the ability to freehand draw the areas of risk, so that > the selection process I was suggesting is not of interest. Again, preparing a proto-map for the human digitizer to finish/check may be of great value, both by speeding their workflow and reducing chances for error. Manual-override at key steps would be very important of course. Here is a little demo ps.map script I've thrown together demonstrating the idea. It builds on the Spearfish catchments generated in the (brand new) r.watershed help page example*. All you need to specify is catchments at risk, it does the rest. [*] http://freegis.org/cgi-bin/viewcvs.cgi/*checkout*/grass6/raster/r.watershed/front/description.html?rev=HEAD&content-type=text/html screenshots of output for whole catchment warning and lowlying areas warning: http://bambi.otago.ac.nz/hamish/grass/screenshots/flood_warning_basins.png http://bambi.otago.ac.nz/hamish/grass/screenshots/flood_warning_lowlying.png screenshot of Spearfish catchments: http://grass.itc.it/screenshots/raster.php First we need to generate polygons for low lying ares from each catchment created with the r.watershed help page example: # create danger polygons for each catchment # (homebrew example of predictor for at-risk lowlying areas) r.cost -k in=slope out=slope_cost_from_rivers start_rast=rwater.course r.colors slope_cost_from_rivers col=bcyr -e # choose some threshold. this could be based on hydrologic model output. # for now just set for lower half of slope-costs in the map eval `r.univar -g slope_cost_from_rivers` r.mapcalc "flood.zones = if(slope_cost_from_rivers < $mean, \ rwater.basin, null() )" # convert to vector areas r.to.vect -s in=flood.zones out=flood_zones feature=area v.db.dropcol map=flood_zones column=label v.db.renamecol map=flood_zones column=value,catchment ################################ # dynamic bits, set by model or interactive selection # (eg scripted 'd.what.* -xft' to highlight areas) # Here we say catchment #6 and #12 are at risk. FLOOD_BASINS=6,12 TIMESTAMP=`date` ############################### # the rest is a static template # commands could be written to a file and then passed to ps.map input= # convert catchment list to SQL query FLOOD_BASIN_SQL=`echo $FLOOD_BASINS | \ sed -e 's/^/catchment = /' -e 's/,/ OR catchment = /g'` # generate PostScript image ps.map out=flood_warning.ps << EOF raster elevation.dem # example of dashed lines vlines roads style 000011 where label ~ 'highway' width 0.25 label Highways end vlines rwater_course color grey label Water courses end vareas rwater_basins #change to "flood_zones" vector map for lowlying areas instead of # entire catchment where $FLOOD_BASIN_SQL color red fcolor red width 2 pat $GISBASE/etc/paint/patterns/diag_up.eps label Catchements subject to flood risk end vlegend end text 100% -3% Warning issued $TIMESTAMP font Helvetica-BoldOblique fontsize 12 ref right end end EOF # convert to PDF ps2pdf flood_warning.ps # convert to PNG pstoimg -antialias -aaliastext -out flood_warning.png -scale 1.3 \ -crop tb flood_warning.ps The PDF output looks the best. Rendering problems: * EPS hatch pattern renders in gv and PNG with black boxes behind lines?? These do not appear in PDF + acrobat reader. * EPS hatch patterns are tiled so fill lines have slightly noticeable breaks. * We need to add something to allow skipping vectors in ps.map's vlegends ideas: labelskip [y|N], test for label='' or 'none' or 'skip'? Hamish __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com _______________________________________________ grassuser mailing list [email protected] http://grass.itc.it/mailman/listinfo/grassuser
