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# GEOMTRANSFORM - Geometry Transformations

Author

  Håvard Tveite

Contact

  havard.tveite@nmbu.no

Table of Contents

- Transformations for simple styling (CLASS STYLE only)

  - bbox

  - centroid

  - end and start

  - vertices

- Labels (LABEL STYLE only)

  - labelpnt and labelpoly

- Expressions and advanced transformations (LAYER and CLASS STYLE)

  - Combining / chaining expressions

    - buffer

  - generalize ([shape], tolerance)

  - simplify([shape], tolerance)

  - simplifypt([shape], tolerance)

  - smoothsia ( [shape], smoothing_size, smoothing_iterations, preprocessing )

    - Tuning the behaviour of smoothsia

    - Dataset resolution is too high

    - Dataset resolution is too low

    - Curves

- Javascript transformation

  - Introduction

  - Usage

    - Example 1. Simple Geomtransform

    - Example 2. Printing logs in MapServer logs

  - Basic API

    - pointObj

      - Constructor

      - Members

      - Methods

    - lineObj

      - Constructor

      - Members

      - Methods

    - shapeObj

      - Constructor

      - Members

      - Methods

Geometry transformations return a new geometry. The purpose of a geometry transformation can be to achieve special effects for symbol rendering and labeling.

Geometry transformation is available at the LAYER level and the STYLE level. At the LAYER level (since 6.4), the original vector geometry (“real world” coordinates) is used. At the STYLE level, pixel coordinates are used.

It may be useful to apply pixel values also at the LAYER level, and that is possible. If UNITS is defined in the LAYER, the [map_cellsize] variable can be used to convert to pixel values at the LAYER level:

    GEOMTRANSFORM (simplify([shape], [map_cellsize]*10))

## Transformations for simple styling (CLASS STYLE only)

The following simple geometry transformations are available at the CLASS STYLE level:

- bbox

- centroid

- end

- start

- vertices

### bbox

- GEOMTRANSFORM bbox returns the bounding box of the geometry.

  - GEOMTRANSFORM “bbox”

Note

Only available for STYLE in the CLASS context.

Geomtransform bbox

Class definitions for the example:

    CLASS
      STYLE
        COLOR 0 0 0
        WIDTH 6
      END # STYLE
      STYLE
        GEOMTRANSFORM "bbox"
        OUTLINECOLOR 255 0 0
        WIDTH 1
        PATTERN 1 2 END
      END # STYLE
    END # CLASS

### centroid

- GEOMTRANSFORM centroid returns the centroid of the geometry.

  - GEOMTRANSFORM “centroid”

Note

Only available for STYLE in the CLASS context.

Geomtransform centroid

Style definitions for the example.:

    STYLE
      GEOMTRANSFORM "centroid"
      COLOR 255 0 0
      SYMBOL circlef
      SIZE 5
    END # STYLE

Symbol definition for the circlef symbol:

    SYMBOL
      NAME "circlef"
      TYPE ellipse
      FILLED true
      POINTS
        1 1
      END # POINTS
    END # SYMBOL

### end and start

- GEOMTRANSFORM end returns the end point of a line.

- GEOMTRANSFORM start returns the start point of a line.

  - GEOMTRANSFORM “start”

  - GEOMTRANSFORM “end” (since END is used to end objects in the map file, end must be embedded in quotes)

The direction of the line at the start / end point is available for rendering effects.

Note

Only available for STYLE in the CLASS context.

Geomtransform start and end usage

Class definitions for the example.

Lower part of the figure:

    CLASS
      STYLE
        GEOMTRANSFORM "start"
        SYMBOL "circlef"
        COLOR 255 0 0
        SIZE 20
      END # STYLE
      STYLE
        COLOR 0 0 0
        WIDTH 4
      END # STYLE
      STYLE
        GEOMTRANSFORM "end"
        SYMBOL "circlef"
        COLOR 0 255 0
        SIZE 20
      END # STYLE
    END # CLASS

Upper part of the figure:

    CLASS
      STYLE
        COLOR 0 0 0
        WIDTH 4
      END # STYLE
      STYLE
        GEOMTRANSFORM "start"
        SYMBOL "startarrow"
        COLOR 255 0 0
        SIZE 20
        ANGLE auto
      END # STYLE
      STYLE
        GEOMTRANSFORM "start"
        SYMBOL "circlef"
        COLOR 0 0 255
        SIZE 5
      END # STYLE
      STYLE
        GEOMTRANSFORM "end"
        SYMBOL "endarrow"
        COLOR 0 255 0
        SIZE 20
        ANGLE auto
      END # STYLE
      STYLE
        GEOMTRANSFORM "end"
        SYMBOL "circlef"
        COLOR 0 0 255
        SIZE 5
      END # STYLE
    END # CLASS

The startarrow symbol definition (endarrow is the same, except for ANCHORPOINT (value for endarrow: 1 0.5):

    SYMBOL
      NAME "startarrow"
      TYPE vector
      FILLED true
      POINTS
        0 0.4
        3 0.4
        3 0
        5 0.8
        3 1.6
        3 1.2
        0 1.2
        0 0.4
      END # POINTS
      ANCHORPOINT 0 0.5
    END # SYMBOL

### vertices

- GEOMTRANSFORM vertices produces the set of vertices of a line (with direction information).

  - GEOMTRANSFORM “vertices”

Note

Only available for STYLE in the CLASS context.

Geomtransform vertices

Class definitions for the example:

    CLASS
      STYLE
        COLOR 0 0 0
        WIDTH 4
      END # STYLE
      STYLE
        GEOMTRANSFORM "vertices"
        SYMBOL "vertline"
        COLOR 0 0 0
        WIDTH 2
        SIZE 20
        ANGLE AUTO
      END # STYLE
    END # CLASS

The vertline symbol definition:

    SYMBOL
      NAME "vertline"
      TYPE vector
      POINTS
        0 0
        0 1
      END # POINTS
    END # SYMBOL

## Labels (LABEL STYLE only)

The following simple geometry transformations are available at the LABEL STYLE level:

- labelpnt

- labelpoly

These are used for label styling (background colour, background shadow, background frame).

Note

The result of using labelpnt is affected by the LAYER LABELCACHE setting. If LABELCACHE is ON (the default), the label will be shifted when a non-zero sized symbol is added using labelpnt.

### labelpnt and labelpoly

- GEOMTRANSFORM labelpnt produces the geographic position the label is attached to. This corresponds to the center of the label text only if the label is in position CC.

  - GEOMTRANSFORM “labelpnt”

- GEOMTRANSFORM labelpoly produces a polygon that covers the label plus a 1 pixel padding.

  - GEOMTRANSFORM “labelpoly”

Note

Only available for STYLE in the LABEL context.

These transformations can be used to make background rectangles for labels and add symbols to the label points.

Geomtransform labelpnt and labelpoly

Class definitions for the example:

    CLASS
      STYLE
        OUTLINECOLOR 255 255 204
      END # STYLE
      LABEL
        SIZE giant
        POSITION UC
        STYLE # shadow
          GEOMTRANSFORM "labelpoly"
          COLOR 153 153 153
          OFFSET 3 3
        END # Style
        STYLE # background
          GEOMTRANSFORM "labelpoly"
          COLOR 204 255 204
        END # Style
        STYLE # outline
          GEOMTRANSFORM "labelpoly"
          OUTLINECOLOR 0 0 255
          WIDTH 1
        END # Style
        STYLE
          GEOMTRANSFORM "labelpnt"
          SYMBOL 'circlef'
          COLOR 255 0 0
          SIZE 15
        END # Style
      END # Label
    END # Class

Symbol definition for the circlef symbol:

    SYMBOL
      NAME "circlef"
      TYPE ellipse
      FILLED true
      POINTS
        1 1
      END # POINTS
    END # SYMBOL

## Expressions and advanced transformations (LAYER and CLASS STYLE)

### Combining / chaining expressions

A geometry transformation produces a geometry, and that geometry can be used as input to another geometry transformation. There are (at least) two ways to accomplish this. One is to combine basic geometry transformation expressions into more complex geometry transformation expressions, and another is to combine a geometry transformation expression at the LAYER level with a geometry transformation expressions or a simple geometry transformation at the CLASS STYLE level.

Combining geometry transformation expressions A geometry transformation expression contains a [shape] part. The [shape] part can be replaced by a geometry transformation expression.

For example:

    GEOMTRANSFORM (simplify(buffer([shape], 20),10))

In this transformation, buffer is first applied on the geometry ([shape]). The resulting geometry is then used as input to simplify.

A style that demonstrates this:

    STYLE
      GEOMTRANSFORM (simplify(buffer([shape], 20),10))
      OUTLINECOLOR 255 0 0
      WIDTH 2
    END # STYLE

The result of this transformation is shown at the top of the following figure (red line). The original polygon is shown with a full black line and the buffer with a dashed black line.

Combining expressions with simple geometry transformations Simple geometry transformations are only available for CLASS STYLE, but can be combined with geometry transformation expressions at the LAYER level.

Excerpts from a layer definitions that does this kind of combination:

    LAYER
      ...
      GEOMTRANSFORM (simplify(buffer([shape], 10),5))
      CLASS
        ...
        STYLE
          GEOMTRANSFORM "vertices"
          COLOR 255 102 102
          SYMBOL vertline
          SIZE 20
          WIDTH 2
          ANGLE auto
        END # STYLE
      END # CLASS
    END # LAYER

The result of this transformation is shown at the bottom of the following figure (the red lines). The result of the LAYER level geomtransform is shown with a full black line. The original polygon is the same as the one used at the top of the figure.

Combining geomtransform expressions

#### buffer

- GEOMTRANSFORM buffer returns the buffer of the original geometry. The result is always a polygon geometry.

  - GEOMTRANSFORM (buffer ([shape], buffersize))

Note

Negative values for buffersize (setback) is not supported.

Note

Can be used at the LAYER level and for STYLE in the CLASS context.

Note

Buffer does not seem to work for point geometries.

Geomtransform buffer

Some class definitions for the example.

Lower part (polygon with buffers):

    CLASS
      STYLE
        OUTLINECOLOR 0 255 0
        GEOMTRANSFORM (buffer([shape], 20))
        WIDTH 1
      END # STYLE
      STYLE
        OUTLINECOLOR 0 0 255
        GEOMTRANSFORM (buffer([shape], 10))  #
        WIDTH 1
      END # STYLE
      STYLE
        COLOR 255 0 0
        GEOMTRANSFORM (buffer([shape], 5))  #
      END # STYLE
      STYLE
        COLOR 0 0 0
      END # STYLE
    END # CLASS

Upper right part (layer level geomtransform):

    LAYER  # line buffer layer
      STATUS DEFAULT
      TYPE LINE
      FEATURE
        POINTS
          80 70
          80 75
        END # Points
      END # Feature
      GEOMTRANSFORM (buffer([shape], 10))
      CLASS
        STYLE
          COLOR 0 0 255
        END # STYLE
      END # CLASS
    END # LAYER

### generalize ([shape], tolerance)

- GEOMTRANSFORM generalize simplifies a geometry ([shape]) in a way comparable to FME’s ThinNoPoint algorithm. See http://trac.osgeo.org/gdal/ticket/966 for more information.

  - GEOMTRANSFORM (generalize([shape], tolerance))

  tolerance is mandatory, and is a specification of the maximum deviation allowed for the generalized line compared to the original line. A higher value for tolerance will give a more generalised / simplified line.

Note

Can be used at the LAYER level and for STYLE in the CLASS context.

Note

Depends on GEOS.

The figure below shows the result of applying generalize at the STYLE level with increasing values for tolerance (10 - green, 20 - blue and 40 - red).

Geomtransform generalize

One of the STYLE definitions for the example (tolerance 40):

    STYLE
      GEOMTRANSFORM (generalize([shape], 40))
      COLOR 255 0 0
      WIDTH 1
      PATTERN 3 3 END
    END # STYLE

### simplify([shape], tolerance)

- GEOMTRANSFORM simplify simplifies a geometry ([shape]) using the standard Douglas-Peucker algorithm.

  - GEOMTRANSFORM (simplify([shape], tolerance))

  tolerance is mandatory, and is a specification of the maximum deviation allowed for the generalized line compared to the original line. A higher value for tolerance will give a more generalised / simplified line.

Note

Can be used at the LAYER level and for STYLE in the CLASS context.

The figure below shows the result of applying simplify at the STYLE level with increasing values for tolerance (10 - green, 20 - blue and 40 - red).

Geomtransform simplify

One of the STYLE definitions for the example (tolerance 40):

    STYLE
      GEOMTRANSFORM (simplify([shape], 40))
      COLOR 255 0 0
      WIDTH 1
      PATTERN 3 3 END
    END # STYLE

### simplifypt([shape], tolerance)

- GEOMTRANSFORM simplifypt simplifies a geometry ([shape]), ensuring that the result is a valid geometry having the same dimension and number of components as the input. tolerance must be non-negative.

  - GEOMTRANSFORM (simplifypt([shape], tolerance))

  tolerance is mandatory, and is a specification of the maximum deviation allowed for the generalized line compared to the original line. A higher value for tolerance will give a more generalised / simplified line.

Note

Can be used at the LAYER level and for STYLE in the CLASS context.

The figure below shows the result of applying simplifypt at the STYLE level with increasing values for tolerance (10 - green, 20 - blue and 40 - red).

Geomtransform simplifypt

One of the STYLE definitions for the example (tolerance 40):

    STYLE
       GEOMTRANSFORM (simplifypt([shape], 40))
       COLOR 255 0 0
       WIDTH 1
       PATTERN 3 3 END
     END # STYLE

### smoothsia ( [shape], smoothing_size, smoothing_iterations, preprocessing )

- GEOMTRANSFORM smoothsia returns a smoothed version of a line.

  - GEOMTRANSFORM (smoothsia ( [shape], smoothing_size, smoothing_iterations, preprocessing ))

  The following parameters are used:

  - shape (mandatory). Specify the geometry to be used

  - smoothing_size (optional). The window size (number of points) used by the algorithm. The default is 3.

  - smoothing_iterations (optional). The number of iterations of the algorithm. The default is 1.

  - preprocessing (optional). Preprocessing method to add more vertices to the geometry prior to smoothing, described below. There are two possible preprocessing methods:

    - all Adds two intermediate vertices on each side of each original vertex. This is useful to preserve the general shape of the line with low resolution data.

    - angle Add vertices at some specific places based on angle detection.

Note

Can be used at the LAYER level and for STYLE in the CLASS context.

Example of a simple layer definition:

    LAYER NAME "my_layer"
    TYPE LINE
    STATUS DEFAULT
    DATA roads.shp
    GEOMTRANSFORM (smoothsia([shape], 3, 1, 'angle'))
    CLASS
      STYLE
        WIDTH 2
        COLOR 255 0 0
      END
    END

Here are some examples showing results with different parameter values.

Original geometry (left) and smoothsia with default parameters (right)

Smoothsia - Larger window size (left) and larger window size with more iterations (right)

#### Tuning the behaviour of smoothsia

smoothsia has several parameters that can be used to tune its behaviour. The following sections describe some cases / possibilities.

#### Dataset resolution is too high

If you are trying to smooth a line that has a very high resolution (high density of vertices at the current view scale), you may not get the expected result because the vertices are too dense for the smoothing window size. In this case you might want to simplify the geometries before the smoothing. You can combine smoothing and simplification in a single geomtransform for that:

    GEOMTRANSFORM (smoothsia(simplifypt([shape], 10)))

See RFC 89: Layer Geomtransform for more info. Here’s a visualization of the issue:

High resolution geometry, smoothing and simplification

#### Dataset resolution is too low

If you are trying to smooth a long line that has a low density of vertices, you may not get the expected result in some situations. You may lose some important parts of the geometry during the smoothing, for instance around acute angles. You can improve the result by enabling a preprocessing step to add intermediate vertices along the line prior to smoothing.

This behavior is controlled using the all value in the preprocessing argument of the smoothsia geomtransform:

    GEOMTRANSFORM (smoothsia([shape], 3, 1, 'all'))

This preprocessing will be performed before the smoothing. It adds 2 intermediate vertices on each side of each original vertex. This is useful if we really need to preserve the general shape of the low resolution line. Note that this might have an impact on the rendering since there will be more vertices in the output.

Here’s a visualization of the issue:

Effects of normal smoothing and preprocessing

#### Curves

The preprocessing step might not be appropriate for all cases since it can impact the smoothing result significantly. However, without it, you might notice bad smoothing for curved lines with large distances between the line vertices. See this example:

Effects of normal smoothing (without preprocessing)

You can improve that by enabling another type of preprocessing: angle. This one will add points at some specific places based on angle detection to recognize the curves. Here’s how you can enable it:

    GEOMTRANSFORM (smoothsia([shape], 3, 1, 'angle'))

The use of angle with smoothsia

## Javascript transformation

Author

  Alan Boudreault

Contact

  aboudreault at mapgears.com

Last Updated

  2013/16/12

### Introduction

Using GEOMTRANSFORM this way makes it possible to modify the geometry programmatically in addition to the built-in geomtransform functions.

### Usage

Simply declare the javascript plugin this way:

    MAP
      ...
      LAYER
      ...
        GEOMTRANSFORM "javascript://transform.js" # relative path
        CLASS
        END
      END
    END

The path can also be absolute.

    MAP
      ...
      LAYER
      ...
        GEOMTRANSFORM "javascript:///home/user/transform.js" # absolute path
        CLASS
        END
      END
    END

The javascript plugin has to implement a function named geomtransform that will be automatically called. This function has to return a new shape. Note that only the geometry of this new shape will be used, so your original shape attributes will be preserved.

Access to the feature attributes is made through the `shape.attributes` javascript object.

The following javascript functions are available:

- alert(str1, str2, …, str)

    print some text in MapServer logs

- print(str1, str2, …, str)

    print some text in MapServer logs

- require(path_to_lib1, path_to_lib2, …, path_to_lib)

    include one or more javascript lib

#### Example 1. Simple Geomtransform

This example does a simple vertical translation …

    function geomtransform() {
      new_shape = new shapeObj();
      new_shape.add(new lineObj());
      new_point = new pointObj();
      new_point.x = shape.line(0).point(0).x;
      new_point.y = shape.line(0).point(0).y+30000;
      new_shape.line(0).add(new_point);
      return new_shape;
    }

#### Example 2. Printing logs in MapServer logs

Extends example 1 by printing information to the MapServer log.

    MAP
      ...
      CONFIG  "MS_ERRORFILE" "/tmp/mapserver.log"
      DEBUG 1
      LAYER
      ...
         GEOMTRANSFORM "javascript://transform.js"
      ...
      END
    END

    function geomtransform() {
      new_shape = new shapeObj();
      new_shape.add(new lineObj());
      new_point = new pointObj();
      new_point.x = shape.line(0).point(0).x;
      new_point.y = shape.line(0).point(0).y+30000;
      print('Modified y value from: ' + shape.line(0).point(0).y + ' to: '+new_point.y);
      new_shape.line(0).add(new_point);
      return new_shape;
    }

### Basic API

A minimal API is currently available to create a new shape.

#### pointObj

##### Constructor

    new pointObj()

##### Members

Type | Name | Note
--- | --- | ---
double | x |
double | y |
double | z |
double | m |

##### Methods

void setXY(double x, double y[, double m])

  Set the x,y[,m] values.

void setXYZ(double x, double y, double Z[, double m])

  Set the x,y,z[,m] values.

#### lineObj

##### Constructor

    new lineObj()

##### Members

Type | Name | Note
--- | --- | ---
int | numpoints | read-only

##### Methods

pointObj point(int index)

  Returns the point at the index position.

void add(pointObj point)

  Add a point to the line.

void addXY(double x, double y[, double m])

  Add point to the line from an x,y[,m] values.

void addXYZ(double x, double y, double Z[, double m])

  Add point to the line from an x,y,z[,m] values.

#### shapeObj

##### Constructor

    new shapeObj(int type)

‘type’ is one of shapeObj.Point, shapeObj.Line, shapeObj.Polygon or shapeObj.Null

##### Members

Type | Name | Note
--- | --- | ---
int | numvalues | read-only
int | numlines | read-only
int | index | read-only
int | type | read-only
int | tileindex | read-only
int | classindex | read-only
text | text |
object | attributes |

##### Methods

shapeObj clone()

  Returns a clone of the shape.

lineObj line(int index)

  Returns the line at the index position.

void add(lineObj line)

  Add a line to the shape.

void setGeometry(shapeObj shape)

  Replace the geometry of the object with the shape geometry.