arcgis-10.0arcpy
I have a drainage density map and i want to interactively retrieve watershed by clicking a point on map. Once I zoomed to an area of interest and click the highest accumulation point of my choice then i get in return watershed only encompassing that outlet. I am wondering if anyone had already done that manually or automatically. Any suggestion to do it will be helpful.
Thanks.
The way that ArcGIS computes watersheds probably doesn't match with your intuition: only areas upland of a specific pourpoint will drain to that spot, so if you locate the pour point at the center of the lake, 'lower' elevation spots drain into other basins. As Dan mentioned, instead you want to locate it at the top of the outflow stream, where the water from the lake heads to rivers below.
Another option to produce this effect is to continue locating the pour point in the center of the lake, but build an artificial 'dam' at the bottom of the watershed by 'burning': create a new line feature, convert it to a raster with a large value (say, 300). Now the DEM should be forced to empty at your desired pour, with the only artifacts being introduced by the manually produced dam itself.
If you're looking for something more sophisticated, you may want to look into the ArcHydro tools (beta version for ArcGIS 10), which provide a more detailed set of tools for working with hydrologic features -- see this tutorial for details.
EDIT:
Ok, I took another swing at it now that I think I have more of an idea of what you're looking for. It isn't perfect, as you can't select specific existing values, but you CAN select a field and enter as many values as you want into the query. Here's the code:
import arcpy
from arcpy.analysis import *
#Define input/output
input = arcpy.GetParameterAsText(0)
fieldName = arcpy.GetParameterAsText(1)
values = arcpy.GetParameterAsText(2)
output = arcpy.GetParameterAsText(3)
#Build the where clause
queryJoin = "' OR " + fieldName + " = '"
whereClause = fieldName + " = '" + queryJoin.join(values) + "'"
Select(input, output, whereClause)
When you set up your parameters, make sure that the field parameter is 'obtained from' "input". Also make sure you select "yes" for multi value for the values parameter.
This will give you something very similar to the example you linked to. I'm sure the query building could be done a better way but my brain is fried. Let me know if this is more along the lines of what you were looking for.
Best Answer
To do this I think you need to use:
UPDATE
I do not have a Spatial Analyst license to test the Snap Pour Point and Watershed parts, but I just tested the Feature Set parameter to ask a user to input a point using the cursor on a map, and then buffer it. This demonstrates the remaining bit that seems to be causing you problems.
The Python script (test.py) is:
I then created a point feature class with the correct coordinate system to act as the schema for the point I want to Buffer (or in your case to Snap Pour Point then Watershed).
When I used Add Script to create a tool from test.py I just gave it one parameter:
With that done I run the tool, which gives me the chance to click on the map to create a point geometry that gets passed to the Python script to Buffer it.