topic Re: Differences between results obtained with Raster Calculator and Map Algebra (VB) in ArcGIS Spatial Analyst Questions

Differences between results obtained with Raster Calculator and Map Algebra (VB)

CarlesMiquel — Thu, 07 Aug 2014 14:05:31 GMT

Hello,

I would want to work with Map Algebra launched in VB from ArcGis 9.3.

The results obtained, are a little bit different from those obtained with Raster Calculator.

Does someone know where could be the problem?

Thank you very much,

Carles.

Re: Differences between results obtained with Raster Calculator and Map Algebra (VB)

DanPatterson_Retired — Thu, 07 Aug 2014 16:15:31 GMT

Examples would be great...the syntax and the outputs would be useful

Re: Differences between results obtained with Raster Calculator and Map Algebra (VB)

curtvprice — Thu, 07 Aug 2014 18:11:02 GMT

If the same map algebra expression generates different results when called from different environments (for example, from running the 9x Raster Calculator tool, ModelBuilder, or using a geoprocessing tool), I believe a good place to start is to verify the environments used -- cell size, extent, coordinate system, etc. -- and make sure they are the same.

In 9.x this is particularly problematic as the the Raster Calculator (and VB/VBA calls to RasterOp objects) observe the ArcObjects settings (set in the Spatial Analyst toolbar Options), while the map algebra geoprocessing tools (SOMA, MOMA) use the (perhaps different) settings in the geoprocessing environment. In 10.x, all spatial analyst tools use the geoprocessing environment -- much less confusing that way!

Re: Differences between results obtained with Raster Calculator and Map Algebra (VB)

CarlesMiquel — Fri, 08 Aug 2014 12:09:31 GMT

Thank you to both,

I am sure you are right Curtis, but I don't know how the environment settings could be fixed in VBA for Map Algebra. As suggested by Dan, I attach the code used just in case it could help to bring more information.

Thank you very much,

Carles.

Sub Map_algebra_calculation(calculation_text As String, Output_raster_name As String)

strData = "C:\OUTPUT_PATH\"

Dim pMxDoc As IMxDocument

Set pMxDoc = ThisDocument

Dim pMap As IMap

Set pMap = pMxDoc.FocusMap

Dim pRLayer As IRasterLayer

Dim pLayer_AAA As ILayer

Dim pInRaster_AAA As IRaster

Dim pLayer_BBB As ILayer

Dim pInRaster_BBB As IRaster

Dim pLayer_CCC As ILayer

Dim pInRaster_CCC As IRaster

Dim pLayer_DDD As ILayer

Dim pInRaster_DDD As IRaster

Dim pLayer_EEE As ILayer

Dim pInRaster_EEE As IRaster

' Create a Spatial operator

Dim pAlgbOp As IMapAlgebraOp

Set pAlgbOp = New RasterMapAlgebraOp

Set pLayer_AAA = pMap.Layer(2)

Set pRLayer = pLayer_AAA

Set pInRaster_AAA = pRLayer.Raster

Set pLayer_BBB = pMap.Layer(3)

Set pRLayer = pLayer_BBB

Set pInRaster_BBB = pRLayer.Raster

Set pLayer_CCC = pMap.Layer(4)

Set pRLayer = pLayer_CCC

Set pInRaster_CCC = pRLayer.Raster

Set pLayer_DDD = pMap.Layer(5)

Set pRLayer = pLayer_DDD

Set pInRaster_DDD = pRLayer.Raster

Set pLayer_EEE = pMap.Layer(6)

Set pRLayer = pLayer_EEE

Set pInRaster_EEE = pRLayer.Raster

' Bind a raster

Call pAlgbOp.BindRaster(pInRaster_AAA, "AAA")

Call pAlgbOp.BindRaster(pInRaster_BBB, "BBB")

Call pAlgbOp.BindRaster(pInRaster_CCC, "CCC")

Call pAlgbOp.BindRaster(pInRaster_DDD, "DDD")

Call pAlgbOp.BindRaster(pInRaster_EEE, "EEE")

' Set output workspace

Dim pEnv As IRasterAnalysisEnvironment

Set pEnv = pAlgbOp

Dim pWS As IWorkspace

Dim pWSF As IWorkspaceFactory

Set pWSF = New RasterWorkspaceFactory

Set pWS = pWSF.OpenFromFile("C:\OUTPUT_PATH\TEMP", 0)

Set pEnv.OutWorkspace = pWS

' Perform Spatial operation

Dim pOutRaster As IRaster

' Defineix les variable de la iteracio de l'Excel llegit

' Dim Texte_calculadora_raster As String

' Set Texte_calculadora_raster = calculation_text

' Dim Nom_fitxer_sortida As String

' Set Nom_fitxer_sortida = Output_raster_name

'aquí comança el càlcul de la regressio multiple

Set pOutRaster = pAlgbOp.Execute(calculation_text) '(Texte_calculadora_raster)

' Unbind rasters

Call pAlgbOp.UnbindRaster("AAA")

Call pAlgbOp.UnbindRaster("BBB")

Call pAlgbOp.UnbindRaster("CCC")

Call pAlgbOp.UnbindRaster("DDD")

Call pAlgbOp.UnbindRaster("EEE")

' Add it into ArcMap

Set pRLayer = New RasterLayer

pRLayer.CreateFromRaster pOutRaster

' Add its name (Output raster name)

pRLayer.Name = Output_raster_name pMap.AddLayer pRLayer

Call createFileFromRaster(pOutRaster, strData + pRLayer.Name)

End Sub

Re: Differences between results obtained with Raster Calculator and Map Algebra (VB)

curtvprice — Fri, 08 Aug 2014 16:53:14 GMT

I don't know how the environment settings could be fixed in VBA for Map Algebra.

I believe these settings are properties on your pEnv (IRasterAnalysisEnvironment) object. I would query your pEnv object and see if the values are the same that were set in the Spatial Analyst toolbar options when you ran the Raster Calculator. it's true the Raster Calculator interface is different from the raster tools and this a major reason it went away at 10.x.

Have you considered eschewing the the ArcObjects Ops and instantiate a geoprocessor object instead so you can use the single-output map algebra tool - this lets the GP do a lot of the work for you -- a lot less code! A side benefit of doing it that way is your code will be a lot more portable to 10.x. Also, note that VBA is deprecated from 10.x on.

Re: Differences between results obtained with Raster Calculator and Map Algebra (VB)

CarlesMiquel — Fri, 30 Jan 2015 09:17:18 GMT

Thank you all.

I am not an expert in programming code and do not know how to set and write this environment.

Could someone posting an example setting all the properties of an pEnv (IRasterAnalysisEnvironment) object?

Thank you very much.

Carles.

Re: Differences between results obtained with Raster Calculator and Map Algebra (VB)

curtvprice — Sat, 11 Dec 2021 17:21:11 GMT

I am not a developer either, but it seems pretty straight forward, along the lines of:

cell_size = 30
Dim pRasEnv as IRasterAnalysisEnvironment
pRasEnv.SetCell(esriRasterEnvValue, cell_size)

I still think going to geoprocessing is an easier path - and more forward-compatible.

Re: Differences between results obtained with Raster Calculator and Map Algebra (VB)

CarlesMiquel — Sat, 31 Jan 2015 21:31:25 GMT

Thank you Curtis,

I will try your example. I tried geoprocessing with an adapted code in the base of this one, but the results are very different from the ones obtained with the raster calculator. I don't know where the problem is.

Do you have an idea?

# Create the Geoprocessor object

gp = arcgisscripting.create()

try:

# Set local variables

InExpression = "focalsum(C:/data/flowdir, Circle, 3)"

OutRaster = "C:/data/soma01"

# Check out Spatial Analyst extension license

gp.CheckOutExtension("Spatial")

# Process: MapAlgebraStatement

gp.SingleOutputMapAlgebra_sa(InExpression, OutRaster)

except:

# If an error occurred while running a tool, then print the messages.

print gp.GetMessages()

Re: Differences between results obtained with Raster Calculator and Map Algebra (VB)

CarlesMiquel — Sat, 31 Jan 2015 22:03:31 GMT

Thank you Curtis,

An how could I define the other parametre from pEnv (Extent as interesection, etc...)?

Re: Differences between results obtained with Raster Calculator and Map Algebra (VB)

CarlesMiquel — Sat, 31 Jan 2015 22:05:32 GMT

Dim gp As Object

Set gp = CreateObject("esriGeoprocessing.GPDispatch.1")

gp.CheckOutExtension "spatial"

gp.AddToolbox "C:/Program Files/ArcGIS/ArcToolbox/Toolboxes/Spatial Analyst Tools.tbx"

Dim StrDataComplerta As String

StrDataComplerta = StrData + nom_raster_sortida

gp.SingleOutputMapAlgebra_sa text_calcul, StrDataComplerta