I apologise if this has been answered before, as it seem like quite a basic question but I couldnt find a solution. (9.3, ArcView license with spatial analyst and 3D analyst).
I am trying to calculate the volume of water that would be impounded by a hypothetical dam using cut/fill, and I am having trouble creating the "after" raster.
I have an elevation raster (Ras1) and a polygon of the surface of the potential reservoir formed by the dam and a 450m contour. I used "extract by mask" to create a raster of the reservoir and reclassified this to a constant 450m (Ras2). I am now trying to create a raster (Ras3) that is identical to Ras1 apart from the area covered by Ras2, which should take the Ras2 values (450)
I have tried using raster calculator an con([Ras1] > 0, [Ras1], [Ras2]) but the output is identical to Ras2, with no data from Ras1.
Where am I going wrong with this? and is this even a sensible method?
Once I have Ras3 I am assuming cut/fill with Ras1 as "before" and Ras3 as "after" will give me the volume
I have found the volume using TIN polygon volume already but I want to compare it with the cut/fill method
I have an elevation raster (Ras1) and a polygon of the surface of the potential reservoir formed by the dam and a 450m contour. I used "extract by mask" to create a raster of the reservoir and reclassified this to a constant 450m (Ras2). I am now trying to create a raster (Ras3) that is identical to Ras1 apart from the area covered by Ras2, which should take the Ras2 values (450)
I have tried using raster calculator an con([Ras1] > 0, [Ras1], [Ras2]) but the output is identical to Ras2, with no data from Ras1.
Where am I going wrong with this? and is this even a sensible method?
Hi Tim,
When using a formula in Spatial Analyst, you should take special care about the NoData values. Normally combining a value with a NoData value results in NoData.
To avoid this try the following formula:
Con ( IsNull ( [Ras2] ) , [Ras1] , [Ras2] )
In this case it detects the NoData values and returns the values from [Ras1], other areas will be filled with the data from [Ras2].
I have an elevation raster (Ras1) and a polygon of the surface of the potential reservoir formed by the dam and a 450m contour. I used "extract by mask" to create a raster of the reservoir and reclassified this to a constant 450m (Ras2). I am now trying to create a raster (Ras3) that is identical to Ras1 apart from the area covered by Ras2, which should take the Ras2 values (450)
I have tried using raster calculator an con([Ras1] > 0, [Ras1], [Ras2]) but the output is identical to Ras2, with no data from Ras1.
Where am I going wrong with this? and is this even a sensible method?
Hi Tim,
When using a formula in Spatial Analyst, you should take special care about the NoData values. Normally combining a value with a NoData value results in NoData.
To avoid this try the following formula:
Con ( IsNull ( [Ras2] ) , [Ras1] , [Ras2] )
In this case it detects the NoData values and returns the values from [Ras1], other areas will be filled with the data from [Ras2].
