select cells according to the focal max and focal min of a 3 x 3 neighborhood: cells where the focal max exceeds 2750 and focal min is less than 2750 are cells through which the 2750 contour line must pass, for example.
Nope, does not help!
The problem with the FAC values is that they seldom increase by 1. You will only find your exact FAC value if you are really really lucky.
Try this:
Use the Con() function to set a 1 for those FAC values higher than you target (lower in the watershed).
Use the Con() function to set a 1 for those FAC values lower than your target (higher in the watershed).
Convert the two resulting rasters to polygons. There will be a gap between the two polygons or their edges will touch. This is where your target would exist if it did exist. It would be the closets you will get to the answer.
Thank you Mark!
That's really old topic - nearly 4 yers old)
Raster for polygons would take ages - I am working with huge NED DEM datasets.
Any raster to vector conversions are exceptionally slow for monster datasets.
As I remember - looking at old saved toolbox - I've finally used to very simple solution suggested earlier:
(1) used Focal statistics with rectangle 2x2 cell filter to generate FocalMaxFlowAccumulation and FocalMinFlowAccumulation grids.
(2) calculated raster where (FocalMaxFlowAccumulation >= ExactValue) AND (FocalMinFlowAccumulation < ExactValue)
(3) Converted cells of step2 raster to points - voila - have found exact locations for given drainage flow accumulation values.
Below is the snapshot of quick-and-dirty model to design stream sediment sampling program for 9 different survey resolution / initial drainage target size scenarios.
!