Reading GeoTIFF with geotools

Question

I have a geotiff file and I use geotools library for parsing it.

This is my code:

File f = new File("myFile.tif");

ParameterValue<OverviewPolicy> policy = AbstractGridFormat.OVERVIEW_POLICY.createValue();
policy.setValue(OverviewPolicy.IGNORE);

ParameterValue<String> gridsize = AbstractGridFormat.SUGGESTED_TILE_SIZE.createValue();
ParameterValue<Boolean> useJaiRead = AbstractGridFormat.USE_JAI_IMAGEREAD.createValue();
useJaiRead.setValue(true);

GridCoverage2D image = new GeoTiffReader(f).read(new GeneralParameterValue[]{policy, gridsize, useJaiRead});

Rectangle2D bounds2D = image.getEnvelope2D().getBounds2D();     
GridGeometry2D geometry = image.getGridGeometry();

System.out.println(geometry);

System.out.println(bounds2D);

The output of geometry is:

GridGeometry2D[
    GeneralGridEnvelope[0..1199, 0..1399], 
    PARAM_MT[
        "Affine", 
        PARAMETER["num_row", 3], 
        PARAMETER["num_col", 3], 
        PARAMETER["elt_0_0", 996.4799194335938], 
        PARAMETER["elt_0_2", -598386.1975402832], 
        PARAMETER["elt_1_1", -999.6777954101562], 
        PARAMETER["elt_1_2", 650290.4111022949]
    ]
]

The output of bounds2D is:

java.awt.geom.Rectangle2D$Double[x=-598884.4375, y=-748758.6635742188, w=1195775.9033203125, h=1399548.9135742188]

What does this information mean?

Answer 1

It means your image is 1200 pixels wide and 1400 pixels high.

(precision truncated for readability) The pixel size is not square, it is 996.47 (meters?) by -999.67. The negative value indicates the axis direction.

The top left corner of the image is -598386.19 ; 650290.41 (meters?)

The same information is written in the bounds information, in a slightly transformed way:

The center of the image bottom left corner is at x=-598884.43, y=-748758.66

//Add 1/2 pixel size, we get the same coordinate as before
-598884.43 +  996.47 / 2 = -598386.19

For the Y, since it is the bottom coordinate, we can validate by doing

// Add 1/2 pixel size + number of pixels * pixel size, we get the same coordinate as before
// Need to handle the negative pixel size adequatly
 -748758.663574219 + (1400 * 999.677795410156) - (999.677795410156 / 2) =  650290.41

At last, you get the image width and height, in meters

1200 pixels * 996.4799194335938 = 1195775.9
1400 pixels * 999.677795410156 = 1399548.9