Manually editing raster pixels

[LauraBrown1]

Hello all,
I was just inquiring to see if anyone knew a way to change a value of a single cell/pixel of a raster file.

Scenario - I have a raster showing the water flow of a river, however, some of the river flow is disrupted because of a road going through it. I wanted to try and change the pixel values to make my raster act like there wasn't a road crossing the river.

Cheers

[JeffreySwain]

You could try Raster Painting under ArcScan.  That can let you change the values of specific cells manually. For more automated processing, perhaps the Reclassify or Con Tool will be better.

[MarkBoucher]

I wanted to try and change the pixel values to make my raster act like there wasn't a road crossing the river.

This is exactly what Arc Hydro does when it "burns in" streams. You can do this manually. Its a bit of work if you just need to lower a few pixels...

Basically, to mimic Arc Hydro, you could make a stream polyline feature class and draw a line segment along the stream through the crossing. In a field for that line, put in a number for adjusting the DEM elevation. Then convert the line to a raster using the adjustment value. Then add or subtract the two rasters and you will lower the DEM elevation. (I think you could do the same thing for a point.)

In Arc Hydro the next steps include filling sinks. If the line elevation was too low to match the lower end flow line, filling the sinks in the DEM will raise the elevation to match the downstream DEM grid elevation. A fill sinks function will also fill other sinks in your DEM, so if you just want to make a local change, you would have to play around with the processing extents for the fill function and then mosaic the result back into the original DEM.

Running fill sinks and then subtracting the original DEM from the filled DEM is a good way to find other places where you might have road crossings "blocking" your streams.

[LauraBrown1]

Thanks, that is really helpful! Ill will fiddle around with your suggestion.
It also looks like Arc Hydro is free for 10.1 !

[MarkBoucher]

As far as I know, Arc Hydro has always been free. It does require Spatial Analyst.