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Date:         Wed, 12 Mar 2003 14:05:39 -0800
Reply-To:     Dave Hockman-Wert <[log in to unmask]>
Sender:       Biological Conservation and GIS <[log in to unmask]>
From:         Dave Hockman-Wert <[log in to unmask]>
Subject:      Re: hydrologic modeling extension
In-Reply-To:  <[log in to unmask]>
Content-Type: text/plain; charset=us-ascii

Some of you may remember my post a few months ago that expressed frustration with the ESRI ArcGIS Hydrology Modeling tool. In particular, I found the Watershed button to be most unhelpful (see original post below). Well, I'm happy to inform this list that Kevin Johnston and others at ESRI have updated the Hydrology Modeling tool so that it now includes the option to accept the actual point that is clicked on. It can still "snap" to a point of higher Flow Accumulation as well, but it doesn't force that as the only option. Documentation describing the tool and its uses is also available with the updated version. You can download the file with all of the necessary Visual Basic scripts at the ArcObjects website -- Navigate to Samples/Spatial Analyst/Hydrology Modeling by clicking on the aforementioned folders in the left-hand column. ESRI did not update the tool because of my concerns, but I certainly appreciate the serendipity. Dave --- Dave Hockman-Wert <[log in to unmask]> wrote: > Hi all, > > While the hydrologic modeling extension can be very > helpful, beware the "Watershed" button in ArcGIS. > This is the one that is set up by entering the Flow > Direction and Flow Accumulation grids in the > "Properties" section. Then, when the "Watershed" > button is selected, you can click on a point and it > will produce the "watershed" from that pour point. > > Only it doesn't start from the point you actually > click. I don't know Visual Basic very well, but I > can > read the code well enough to see that it actually > snaps to the point of highest flow accumulation > within > a radius of a certain number of pixels. (I don't > know > how many pixels.) > > So what happens, for example, is that you click on a > point at the downstream end of a tributary, just > before the junction, and it actually produces a > watershed starting on a point along the main stem a > few pixels downstream of the tributary junction. > This > is very unhelpful. > > In my experience, none of the other commands are a > problem. But if you want to generate watershed(s) > from specific points, use the “watershed” command in > Map/Raster Calculator. (Create a grid of pour > points > and use that as the source grid.) > > If anyone else has had a different experience with > this button, I’d be happy to hear about it. > > Regards, > Dave Hockman-Wert __________________________________________________ Do you Yahoo!? Yahoo! Web Hosting - establish your business online ********************************************************** CONSGIS LISTSERV To unsubscribe send to [log in to unmask] this email message SIGNOFF CONSGIS Questions? Contact Pete August, [log in to unmask] **********************************************************

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