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Paul Nicholls · Guest

Hi all, I am making a .bt file reader for a certain type of terrain (see
http://www.vterrain.org/Implementation/Formats/BT.html)

Using the info at that page, I have come up with a unit to help me with this
so far:

unit BTTerrainUnit;

interface

type
TBTTerrainHeader = packed record
Version: array[0..9] of Char;
ColumnsWidth: LongWord;
RowsHeight: LongWord;
DataSize: Word;
FloatingPointFlag: Word;
HorizontalUnits: Word;
UTMZone: Smallint;
Datum: Word;
LeftExtent: Double;
RightExtent: Double;
BottomExtent: Double;
TopExtent: Double;
ExternalProj: Word;
Scale: Single;
Unused: array[0..190-1] of Byte;
end;

function GetHeightDataAt(BTHeader: TBTTerrainHeader; DataStart: Pointer;
x,z: Integer): Double;

implementation

type
PSmallIntArray = ^SmallIntArray;
SmallIntArray = packed array[0..(MaxInt div SizeOf(SmallInt)) - 1] of
Smallint;

PSingleArray = ^SingleArray;
SingleArray = packed array[0..(MaxInt div SizeOf(Single)) - 1] of Single;

PIntegerArray = ^IntegerArray;
IntegerArray = packed array[0..(MaxInt div SizeOf(Integer)) - 1] of
Integer;

PDoubleArray = ^DoubleArray;
DoubleArray = packed array[0..(MaxInt div SizeOf(Double)) - 1] of Double;

function GetHeightDataAt(BTHeader: TBTTerrainHeader; DataStart: Pointer;
x,z: Integer): Double;
begin
if(BTHeader.DataSize = 2)then
begin
if(BTHeader.FloatingPointFlag = 1)then
// single data type
Result := PSingleArray(DataStart)[x+z*BTHeader.ColumnsWidth]
else
// smallint data type
Result := PSmallIntArray(DataStart)[x+z*BTHeader.ColumnsWidth];
end
else
if(BTHeader.DataSize = 4)then
begin
if(BTHeader.FloatingPointFlag = 1)then
// double data type
Result := PDoubleArray(DataStart)[x+z*BTHeader.ColumnsWidth]
else
// integer data type
Result := PIntegerArray(DataStart)[x+z*BTHeader.ColumnsWidth];
end;
end;

end.

My problem is this:

I load a .bt file that I downloaded from here
(http://vterrain.org/data/crater_0513.zip)
into a TMemoryStream

I then do this

ms.Position := 0;
ms.Read(BTHeader,SizeOf(BTHeader));

ms.Position := 0;
DataStart := Pointer(Integer(ms.Memory)+ms.Position); //DataStart is
a pointer to the data straight after the header info...

but it appears that when I iterate through the width and height info I get
from the BTHeader, and call this function GetHeightDataAt(...), I am only
getting 0 values from it...

Can anyone see if I have made a mistake with the GetHeightDataAt(..)
function other defs in the short unit?

I can't see where the problem is :(

Thanks in advance,
Paul Nicholls (Delphi 5/6 Professional)
"The plastic veneer of civilization is easily melted in the heat of the
moment" - Paul Nicholls
[email]paul-nicholls (AT) hotmail (DOT) com[/email]

Replace '-' with '_' to reply

Paul Nicholls · Guest

Don't worry about it guys, I totally rewrote my little unit to do the
reading of the .bt info differently and return it in a 2d array, and it now
works fine :)

Here it is if anyone is interested...

<Unit Code Start>

unit BTTerrainUnit;

interface

uses
Classes,TerrainTypesUnit;

procedure ReadBTHeightDataFromStream(s: TStream; var HeightData:
TDoubleBuffer; var Columns,Rows: Integer);

implementation

const
BTVer11 = 'binterr1.1';
BTVer13 = 'binterr1.3';

type
TBTVersion = array[0..9] of Char; //10

procedure ReadBTHeightDataFromStream(s: TStream; var HeightData:
TDoubleBuffer; var Columns,Rows: Integer);
var
BTVersion: TBTVersion;
DataSize: Word;
FloatingPointFlag: Word;
x,z: Integer;
Value_Single: Single;
Value_Double: Double;
Value_SmallInt: SmallInt;
Value_Integer: Integer;
p: Integer;
begin
p := s.Position;

s.Read(BTVersion,SizeOf(BTVersion));
s.Read(Columns,SizeOf(Columns));
s.Read(Rows,SizeOf(Rows));
s.Read(DataSize,SizeOf(DataSize));
s.Position := p+256;

SetLength(HeightData,Rows,Columns);

for x := 0 to Columns - 1 do
for z := 0 to Rows - 1 do
begin
if(DataSize = 2)then
begin
if(FloatingPointFlag = 1)then
// single data type
begin
s.Read(Value_Single,SizeOf(Value_Single));
HeightData[(Columns - 1)-z,x] := Value_Single;
end
else
// smallint data type
begin
s.Read(Value_SmallInt,SizeOf(Value_SmallInt));
HeightData[(Columns - 1)-z,x] := 1.0*Value_SmallInt;
end;
end
else
if(DataSize = 4)then
begin
if(FloatingPointFlag = 1)then
// double data type
begin
s.Read(Value_Double,SizeOf(Value_Double));
HeightData[(Columns - 1)-z,x] := Value_Double;
end
else
// integer data type
begin
s.Read(Value_Integer,SizeOf(Value_Integer));
HeightData[(Columns - 1)-z,x] := 1.0*Value_Integer;
end;
end;
end;
end;

end.

<Unit Code Start/>

"Paul Nicholls" <.> wrote