Bentley Descartes - Raster Transformation

Pascal Cloutier — Thu, 19 Mar 2020 12:38:39 GMT

Current Revision posted to ContextCapture | Descartes | Pointools | Orbit Wiki by Pascal Cloutier on 3/19/2020 12:38:39 PM

Raster Transformation

Bentley Descartes has many functionalities to transform a raster. This set of tools differ from the raster edit tools in that they don't modify the pixels' value of an image but its form and content. These functions can be found in the Descartes Raster Control tool bar.

Move Raster / Scale Raster / Rotate Raster

The Move Raster, Scale Raster and Rotate Raster tools do basic transformations on the raster. These three operations are found in the Transform Raster tool or as separate tools in the Descartes Raster Control toolbox.

Anchor Point

Found in the Transform Raster tool, the anchor point can be used with the scale or rotate tools to determine the location that will remain fixed or pinned in position.

Productivity tip : Instead of moving the image after a scale or rotation operation use the anchor point.

Mirror

As the name implied, the Mirror tool is used to mirror the selected raster.

Mirror About: This option specifies the axis to use for the mirror operation. The available options are: Horizontal, Vertical and Line. The Line option allows you to define the mirror line by entering two data points.
Mirror Position: This option can be used to specify the positioning mode of the mirror axis.

Warp

The Warp Raster tool allows you to apply a move, scale, rotate or skew transformation or a combination of all those by specifying source to destination relationships.

Method: This specifies the type of geometric transformation to use for the warp operation. Each method uses a different combination of operations and minimum number of required points to define the operation.

Example

For example, let's say you want to fit an image in a rotated rectangle as show in the graphic below.

Since the rectangle doesn't have the same height / width ratio as the image, an affine transformation must be used. An affine transformation can be defined with at least three source-to-destination relationships which are entered as pairs of data points. The defined relationships and the resulting warped image are shown in the graphic below :

Productivity Tip : A warp using the Align, Helmert, and Similitude modes can also done using the basic Move, Scale and Rotate tools. However, when the source-to-destination relationships are known (i.e. : the position, scale and orientation of the image) it's easier and faster to use the Warp tool rather than attempting to do the same with the Move, Scale and Rotate tools.

Square

The Square tool is used to rotate a raster image by squaring a horizontal, vertical, or diagonal axis.

Axis: This option allows you to set which axis to square the image about. The options are: Horizontal, Vertical and 2 Lines.
Attach Copy: Turning this on will create a new attachment of the image.
Resample: When this is on, the image is automatically resampled after the square operation.

Crop

The Crop tool allows you to remove excess pixels on the outside of a specified area. The result of a crop operation is visually identical to a clip operation, the difference being that the cropping operation modifies the source file while clipping doesn't.

Area: The method used to specified the cropping area, which can be one of the following: Block, Oriented Block, Element, and Shape.
Warp to area: The resulting cropped image will be warped to the smallest rectangular area enclosing the crop area.
Work in Image Plane
Use Fence: Use the defined fence for cropping the image.

Warp to Area

This section demonstrates the use of the Warp to Area option. The original image with the element defining the crop area is shown below.

When the Warp to Area option is off, the resulting image is created by placing a rectangular non-oriented block around the crop area and copying the pixels found in that block in the source image to the destination image. The pixels in the block, but not in the cropped area, are set to black. The image below shows the resulting image and its border in magenta.

When the Warp to Area option is on, the resulting image is created by placing a rectangular oriented block around the crop area that minimize the size of the resulting image and warping the pixels found in that block in the source image to the destination image. The image below shows the resulting image and its border in magenta.

As you can see, the resulting image in this example is much smaller when the area option is on then off (i.e. : 82 kB compared to 152 kB, almost twice as small).

Productivity Tip : Use the Warp to Area option for diminishing the size of the file resulting from a crop operation. The more the crop area is diagonal in shape, the more the saving in space.

Resize Canvas

The Resize Canvas tool is used to enlarge or reduce the size of a raster.

Merge

The Merge tools is used to merge several rasters and vectors element together so as to form only one raster.

Options Group Pane

In this pane you can set all special options related to the merge operation.

Element to process: Select if rasters, vectors or both rasters and vectors found in the merge area will be merge. Vectors are merge using the rasterize technology of Descartes.
Use Line Mapping
Create New Attachment(s): Automatically attach the raster resulting from the merge operation.
Fill Clipped Area: If On, the clipped area will be filled with the MicroStation background color, otherwise the extents of the merged area will be rasterized.

Resolution Group Pane

In this pane you can set the resolution of the resulting raster. This settings is important because the rasters merged together can have different resolutions. Usually choosing a resolution twice as high as the highest resolution of all merged rasters will ensure that there is no loss in quality for all merged rasters.

Output Group Pane

In this pane you can set the options related to the raster created for the merge operation.

Output type: Select if the merged elements will be written in one single raster file or multiple raster files, and the file format.
Output Options: Set standard output options like compression, color space, etc...
Grid Definition: Defines the DGN file of the grid definition that should be used for determining the multiple raster files' boundaries.
Model: Defines the specific model in the DGN file containing the grid definition to use.

Corridor

The Corridor tool allows user to copy all the rasters or parts of rasters from an area to another area. This destination and source areas are defined with standard MicroStation elements.

Options: Select if the clip and transparent options in Raster Manager will be turn on or off for the newly created raster.
Output Image Parameters: Select the pixel size of the destination image and the transformation model used to resample the source data to the destination area.
DGN Elements: Select if the DGN elements in the source area will be copy to the destination area depending on if those elements are inside or overlap the area, and if overlap, if they are going to be clipped to the destination area or not.

Tags: Descartes, Database Interface