Overview

The LAS product server is typically used to generate images.  Along with those images, various other files are saved in the output/ directory including -- if the operations requests it -- information describing the relationship between pixels on the image and the real world coordinates they represent.  This information is stored in an xml file in the output/ directory as 'unique_ID_map_scale'.

This information is particularly useful to client pages that use javascript to create clickable or rubber-bandable maps from the LAS images.

Requesting map_scale results in operationsV7.xml

In order to take advantage of this capability, each operation that wishes to access the ~_map_scale response must request that it be generated by listing it in the <response ...> section of the definition of the operation in operationsV7.xml.  Here is an example:

<operation name="Color plot" ID="Plot_2D_XY" output_template="output" service_action="Plot_2D_XY" order="0100">
    <service>ferret</service>
    <response ID="PlotResp">
        <result type="image" ID="plot_image" streamable="true" mime_type="image/png" file_suffix=".gif" />
        <result type="ps" ID="plot_postscript" streamable="true" mime_type="application/postscript" file_suffix=".ps"/>
        <result type="image" ID="ref_map" file_suffix=".gif" />
        <result type="map_scale" ID="map_scale" file_suffix=".xml"/>
        <result type="debug" ID="debug" file_suffix=".txt"/>
        <result type="cancel" ID="cancel" file_suffix=".txt"/>
    </response>
    <region>
        <intervals name="xy" />
    </region>
    <grid_types>
        <grid_type name="regular" />
    </grid_types>
    <optiondef IDREF="Options_2D_image_contour_xy"/>
</operation>

The map_scale.xml file

When LAS prforms an operation that requests a map_scale result a file similar to the following will be found in the output/ directory:

<?xml version="1.0" encoding="UTF-8"?>
<map_scale>
  <x_pixels_per_inch>63.607452</x_pixels_per_inch>
  <y_pixels_per_inch>63.555115</y_pixels_per_inch>
  <x_image_size>560.0</x_image_size>
  <y_image_size>640.0</y_image_size>
  <x_plot_size>420.06363</x_plot_size>
  <y_plot_size>461.91858</y_plot_size>
  <x_offset_from_left>76.32895</x_offset_from_left>
  <y_offset_from_bottom>88.97716</y_offset_from_bottom>
  <x_offset_from_right>63.607452</x_offset_from_right>
  <y_offset_from_top>88.97716</y_offset_from_top>
  <x_axis_lower_left>44.25</x_axis_lower_left>
  <y_axis_lower_left>-57.17</y_axis_lower_left>
  <x_axis_upper_right>116.25</x_axis_upper_right>
  <y_axis_upper_right>22.076</y_axis_upper_right>
</map_scale>

The elements defined in <map_scale> have the following interpretation:

x_pixels_per_inch

number of pixels per 'virtual inch' on the device generating the plot.  This values is not very useful to developers.

y_pixels_per_inch

See above.

x_image_size

width in pixels of the image

y_image_size

height in pixels of the image

x_plot_size

width in pixels of the plotted area  excluding margins on the left and right.

y_plot_size

height in pixels of the plotted area excluding margins on the top and bottom.

x_offset_from_left

number of pixels between the left edge of the image and the left edge of the plotted area  (equivalent to the left margin width)

y_offset_from_bottom

number of pixels between the bottom of the image and the bottom edge of the plotted area  (equivalent to the bottom margin height)

x_offset_from_right

 number of pixels between the right edge of the image and the right edge of the plotted area  (equivalent to the right margin width)

y_offset_from_top

 number of pixels between the top of the image and the top edge of the plotted area  (equivalent to the top margin height)

x_axis_lower_left

world coordinate X value associated with the lower left corner of the plotted area (for XY maps = westernmost longitude)

y_axis_lower_left

world coordinate & value associated with the lower left corner of the plotted area (for XY maps = southernmost latitude)

 x_axis_upper_right

 world coordinate X value associated with the upper right corner of the plotted area (for XY maps = easternmost longitude)

y_axis_upper_right

 world coordinate & value associated with the upper right corner of the plotted area (for XY maps = northernmost latitude)

Using map_scale information in a Velocity template

In order to create a clickable or rubber-bandable product you will need to access these values inside a Velocity template.  The entire map_scale class is available within the Velocity template context as seen in the following snippet:

...

'plot_area' : {                              // defining the plot region within the image
  'offX' : $las_map_scale.getXOffsetFromLeft(),
  'offY' : $las_map_scale.getYOffsetFromTop(),
  'width' : $las_map_scale.getXPlotSize(),
  'height' : $las_map_scale.getYPlotSize()
 },

...

Each element of the map_scale object has a getter method whose name is the CamelCase, no-underscore version of the XML element name.