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iMOD User Manual version 4.4 (html)


9.5IDF-files

The file syntax of IDF-files (iMOD Data Files) is based on a file structure without any line feeds. This means that all data is written direct after each other. It is not written on a different line, but in a different record. An advantage of such a file structure is the possibility to access data randomly throughout the file (known as direct-access). The fileformat is unformatted and can therefore not be read in a normal TextEditor. It is based on the little-endian data format, as we read the file with records of 4 bytes (or 1 word). Since iMOD 5.0, the IDF file can be written in double-precision as well. In that case, the format of the real values are double precision (float 8) instead of single precision (float 4).

Cond.

Record

Format (bytes)

Variable

Description

1

Integer 4

1271
2296

Lahey Record Length Identification; 1271 is a single precision IDF, 2296 a double precision.

2

Integer 4

NCOL

Number of columns

3

Integer 4

NROW

Number of rows

4

Float 4/8

XMIN

X lower-left-coordinate

5

Float 4/8

XMAX

X upper-right-coordinate

6

Float 4/8

YMIN

Y lower-left-coordinate

7

Float 4/8

YMAX

Y upper-right-coordinate

8

Float 4/8

DMIN

Minimal data value

9

Float 4/8

DMAX

Maximal data value

10

Float 4/8

NODATA

NoData value

11

Integer 1

IEQ

0: equidistant IDF
1: nonequidistant IDF

Integer 1

ITB

0: no usage of TOP and BOT Values
1: usage of TOP and BOT Values

Integer 1

Not used

Integer 1

Not used

IEQ=0

12

Float 4/8

DX

Column width.

13

Float 4/8

DY

Row height.

ITB=1

12+ABS(IEQ-1)*2

Float 4/8

TOP

Top value if ITB=1

13+ABS(IEQ-1)*2

Float 4/8

BOT

Bot value if ITB=1

IEQ=1

12+ITB*2

Float 4/8

DX(NCOL)

Column width for each column, ranging from west to east

13+ITB*2+NCOL

Float 4/8

DY(NROW)

Row height for each row, ranging from north to south


IREC=10 + ABS(IEQ-1)*2 + IEQ*(NROW+NCOL) + ITB*2 + 1

IREC

Float 4/8

X(:,:)

Value for each cell

IREC
+(NROW*NCOL)

Integer 1

IADIT

Binary number to store optional arguments:
IP1=1: Comments added
IP?=?:

IP1=1

IREC
+(NROW*NCOL)+1

Integer 1

NLINE

Number of lines that contain comments

Char. 4

COMM(NLINE)

Comment for NLINE

Voxel representation The Variables ITB, TOP and BOT are available in order to display an IDF as a Voxel. The word voxel is a contraction of the words VOlume and piXEL. A voxel represents a value on a regular grid in three-dimensional space. IDF-files can represent “voxels” when they have top- and bottom information stored internally. If those IDF-files are used, the internal IDF value per cell (e.g. permeability) will be coloured (using the associated legend) between the stored top and bottom elevation inside the IDF (see example in Section 6.3).