>I noticed that since version 5.5 of MapInfo it is possible to display
>a special file format called MapInfo Grid, very useful to display
>elevation or other interpolated data. The only way to query the grid
>is the Info Tool.
>
>Is this feature (grid querying) accessible via MapBasic? Also, is
>there any way to get all the grid values intersected by a line object
>and to store them in a table?
Here is the part of some sample code I posted earlier that shows how
to query a grid file with MapBasic. Getting all the grid values that
intersect a line object would be a natural extension of this. As I used
to hear 'it is left as an exercise for the student.'
'
********************************************************************************
Include "MapBasic.def"
Include "Icons.def"
'
********************************************************************************
'Declare external functions (all in MIGrid.DLL)
'Note: All MapBasic funtion variables are passed by reference unless
' explicitly defined to be passed directly with the 'ByVal' key word.
'
********************************************************************************
Declare Function GE_OpenGrid Lib "Migrid.dll" (
lpszFilename As String,
ByVal lCacheSize As Integer,
hGrid As Integer) As Logical
Declare Function GE_GetCoordSysInfo Lib "Migrid.dll" (
ByVal hGrid As Integer,
ptchCoordSys As String,
pdMinXVal As Float,
pdMinYVal As Float,
pdMaxXVal As Float,
pdMaxYVal As Float) As Logical
Declare Function GE_GetContinuousMinMax Lib "Migrid.dll" (
ByVal hGrid As Integer,
pdMinZVal As Float,
pdMaxZVal As Float) As Logical
Declare Function GE_GetDimensions Lib "Migrid.dll" (
ByVal hGrid As Integer,
plWidth As Integer,
plHeight As Integer) As Logical
Declare Function GE_StartRead Lib "Migrid.dll" (
ByVal hGrid As Integer) As Logical
Declare Function GE_GetContinuousValue Lib "Migrid.dll" (
ByVal hGrid As Integer,
ByVal lCol As Integer,
ByVal lRow As Integer,
pdValue As Float,
puchIsNull As SmallInt) As Logical
Declare Function GE_EndRead Lib "Migrid.dll" (
ByVal hGrid As Integer) As Logical
Declare Function GE_CloseGrid Lib "Migrid.dll" (
hGrid As Integer) As Logical
'
********************************************************************************
'Declare Local Functions
'
********************************************************************************
Declare Sub Main
Declare Sub GridInfoToolHandler
'
********************************************************************************
'Global Variables
'
********************************************************************************
Global gsPath As String
'
********************************************************************************
'
********************************************************************************
'Sub Main
'
********************************************************************************
'
********************************************************************************
Sub Main
OnError Goto HandleError
Alter ButtonPad "Tools"
Add
Separator
ToolButton
Calling GridInfoToolHandler
Icon MI_ICON_INFO
Cursor MI_CURSOR_CROSSHAIR
DrawMode DM_CUSTOM_POINT
HelpMsg "Retrieve value from grid cell.\nRetrieve grid value"
Show
Exit Sub
HandleError:
Note "Main: " + Error$()
Resume Next
End Sub
'
********************************************************************************
'
********************************************************************************
' Sub GridInfoToolHandler
'
********************************************************************************
'
********************************************************************************
Sub GridInfoToolHandler
OnError Goto HandleError
Dim sCmd As String
Dim i As SmallInt
Dim lVerbose As Logical
Dim x, y As Float
Dim MapWindowID As Integer
Dim lReturn As Logical
Dim hGrid As Integer
Dim sPath As String
Dim ptchCoordSys As String
Dim pdMinXVal, pdMinYVal, pdMaxXVal, pdMaxYVal As Float
Dim pdMinZVal, pdMaxZVal As Float
Dim plWidth, plHeight As Integer
Dim lCol, lRow As Integer
Dim pdValue As Float
Dim puchIsNull As SmallInt
'
********************************************************************************
'Get map window and layer
'
********************************************************************************
MapWindowID = FrontWindow()
If WindowInfo( MapWindowID, WIN_INFO_TYPE) <> WIN_MAPPER Then
Note "Click in a map window."
Exit Sub
End If
For i = 1 To MapperInfo(MapWindowID, MAPPER_INFO_LAYERS)
If LayerInfo(MapWindowID, i, LAYER_INFO_TYPE) =
LAYER_INFO_TYPE_GRID Then
sPath = LayerInfo(MapWindowID, i, LAYER_INFO_PATH)
Exit For
End If
Next
'
********************************************************************************
'Get Grid file name
'
********************************************************************************
sPath = Left$(sPath, Len(sPath)-3) + "MIG"
If Not FileExists(sPath) Then
If FileExists(ProgramDirectory$() + "Nwgrd30.ghl") Then
sPath = Left$(sPath, Len(sPath)-3) + "GRD"
End If
End If
If Not FileExists(sPath) Then
Note "Cannot find grid file " + sPath
Exit Sub
End If
If sPath <> gsPath Then
gsPath = sPath
lVerbose = TRUE
Else
lVerbose = FALSE
End If
'
********************************************************************************
'set MapBasic coordinate system to match map window coordinate system
'
********************************************************************************
sCmd = "Set " + MapperInfo(MapWindowID,
MAPPER_INFO_COORDSYS_CLAUSE_WITH_BOUNDS)
Run Command sCmd
'
********************************************************************************
'Get coordinates of cursor location
'
********************************************************************************
x = CommandInfo(CMD_INFO_X)
y = CommandInfo(CMD_INFO_Y)
Print "X = " + x + ", Y = " + y
'
********************************************************************************
'Open grid file
'
********************************************************************************
lReturn = GE_OpenGrid(sPath, 1024, hGrid)
If Not lReturn Then
Note "Open " + sPath + " failed"
Exit Sub
End If
If hGrid = 0 Then
Note "Open " + sPath + " failed: grid handle = 0"
Exit Sub
End If
If lVerbose Then
Print " Opened " + sPath + " with handle " + hGrid
End If
'
********************************************************************************
'Get grid coordinate system information (especially min and max
coordinates)
'
********************************************************************************
ptchCoordSys = Space$(255) 'Initialize to allocate actually memory.
lReturn = GE_GetCoordSysInfo(hGrid, ptchCoordSys, pdMinXVal,
pdMinYVal, pdMaxXVal, pdMaxYVal)
If lVerbose Then
Print " " + ptchCoordSys
Print " MinXVal = " + pdMinXVal + ", MinYVal = " + pdMinYVal +
", MaxXVal = " + pdMaxXVal + ", MaxYVal = " + pdMaxYVal
End If
'
********************************************************************************
'Get minimum and maximum grid values
'
********************************************************************************
lReturn = GE_GetContinuousMinMax(hGrid, pdMinZVal, pdMaxZVal)
If lVerbose Then
Print " MinZVal = " + pdMinZVal + ", MaxZVal = " + pdMaxZVal
End If
'
********************************************************************************
'Get grid dimensions (rows and columns)
'
********************************************************************************
lReturn = GE_GetDimensions(hGrid, plWidth, plHeight)
If lVerbose Then
Print " Width = " + plWidth + ", Height = " + plHeight
End If
'
********************************************************************************
'Prepare to read grid
'
********************************************************************************
lReturn = GE_StartRead(hGrid)
If lReturn Then
'
********************************************************************************
'Calculate row and column of cursor location
'
********************************************************************************
lCol = (plWidth * (x - pdMinXVal) / (pdMaxXVal - pdMinXVal)) - .5
lRow = (plHeight -
plHeight * (y - pdMinYVal) / (pdMaxYVal - pdMinYVal)) - .5
'
********************************************************************************
'Retrieve and display grid value
'
********************************************************************************
lReturn = GE_GetContinuousValue(hGrid, lCol, lRow, pdValue, puchIsNull)
If lCol < 0 Or lRow < 0 Or lCol >= plWidth Or lRow >= plHeight Then
If pdValue = 0 Then
Print " Value at col: " + (lCol+1) +
", row: " + (lRow+1) + " is undefined."
Else
Print " Value at col: " + (lCol+1) +
", row: " + (lRow+1) + " = " + pdValue +
", but should be undefined."
End If
Else
If puchIsNull Then
Print " Value at col: " + (lCol+1) +
", row: " + (lRow+1) + " is NULL."
Else
Print " Value at col: " + (lCol+1) +
", row: " + (lRow+1) + " = " + pdValue
End If
End If
lReturn = GE_EndRead(hGrid)
Else
Print " StartRead(" + hGrid + ") failed"
End If
lReturn = GE_CloseGrid(hGrid)
Exit Sub
HandleError:
Note "GridInfoToolHandler: " + Error$()
Resume Next
End Sub
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