Module: Maps | website

Maps Module

Overview

Channel maps are spectroscopic images, where the image contains only emission from a certain small range of wavelength or line-of-sight velocity. They are typical for spectroscopic radio observations, but have come into more frequent use also in the optical and infrared spectral ranges. Usually they are presented in an array of many channel maps representing the complete spectral range that has been observed. The full set of spectral data is often referred to as a data cube, since the image can be arranged as slices of a cube.

The Maps Module is divided in three main sections. The dominant region is the display of the channel maps. Above the maps is the main menu and to the right are the parameter tabs. There are three tabs for General parameters, those for an individual selected Channel and for the Output of the channel images (maps).

General Workflow:

In the General Parameters tab the minimum (initial) and maximum (final) velocities are applied. These are then divided in a number of channels that is the product of the number of channels in rows and columns. To set up this grid of channel maps click on the "Re-grid" button in the main menu and confirm. This generates the grid of image windows. Now render by clicking on the Render Button in the Render Module or press Ctrl-S.

Parameter Panels:

General:

Render: This flag controls whether the channel maps are rendered at all. Make sure to have the tick mark set when using the Map Module.

Initial vel: The smallest velocity to be included (can be negative). This is the center velocity of the first channel map (top left in the grid).

Final vel: The highest velocity to be included. This is the center velocity of the last channel map (bottom right in the grid).

Delta (D): This is the width of the velocity channels. If set to zero, then the width is calculated from the difference between the final and initial velocity divided by the number of channels. If set manually, then the channels may be narrower than that or wider, in which case they overlap. The intensity taken into account is constant over the interval, which may or may no be the case for the actual observations.

Rows & Columns: The number of rows and columns that the channel map grid shall have. The total number of channels is then the product of rows and columns.

Transparency: The transparency of the rendered foreground image. It can be changed with the slider to transition between rendered and observed background image. This helps to compare the model with observations.

Light Echo: This function is deprecated.

Difference: Show the difference image subtracting the observed image from the rendered model image.

Export: Export the rendered image in ASCII format for further external processing.

Channel:

Select a particular channel by clicking on the image in the grid view of the channel maps. The selected channel is highlighted by a thin red line. The Channel parameter panel on the right then displays the settings of that particular channel. To view the image of this channel by itself at a larger scale, click on the "Expand" icon in the main menu of the Map Module.

Vel (km/s): The velocity center of this channel.

D vel (km/s): The full width of the velocity channel.

Image: A reference or observed image can be loaded to be compared with the observation. One can transition between the rendered model and the reference image by changing the Transparency in a numerical way (see below) or using the Transparency slider in the General parameter panel (see above). The reference image can be placed and processed using similar attributes as those used in the Selected Window section of the Render Module. Please see the pages on "Data Preparation" and the Render Module for more details on how to use the Location parameters and the image Modifiers.

Output:

The output parameters control the appearance and labeling of the grid image output using the Save Grid or Save Images button in the Main Menu of the Map Module. An example grid output is shown on the right.

CrossHairs: Mark the center of each channel with a cross.

Labels: Label each channel with its central velocity.

Color: The color for the labels. Change the color by clicking on the colored squared. A dialog opens to let you select a different color.

Menu bar:

Re-grid: After you adjusted the General Parameters for the grid of channel maps, the Re-grid button sets up the grid using these parameters. When you change the General Parameters use this button again to apply these parameters.

Insert: Individual channels can be inserted before the currently selected channel. Note that this channel does not change the parameters of the pre-existing channel and is therefore not part of the regular sequence that was established using the Re-grid button. This new channel needs to be set up individually in the Channel parameter panel.

Delete: Delete the currently selected channel.

Save grid & Save images: save the grid of image or individual channel images. Se the section on Output above for details.

Palette: Opens the image adjustment dialog for the channel maps. Here you can adjust brightness, scaling, and add other image modifiers. Note that the Gaussian Blur modifier handles the resolution of the maps. This is currently disconnected from the Seeing parameter in the Render Module and needs to be adjusted separately. In the Maps Module it works in terms of pixels, so it is depends on the resolution. This feature will be improved in a future release.

Properties: Opens the Properties dialog for the detailed appearance of the grid coordinates, tick marks, fonts and colors.

Load obs: Load observed or reference images to the background of the grid. Here you can load a sequence of multiple images to fill all the channels. Select multiple image in the directory dialog that opens by clicking on the first of the sequence and then Shift-click on the last. Reference images for individual channels can be loaded or changed with the corresponding Image load button in the Channel properties panel.

Expand: Expands the selected individual channel image to full size of the image grid area for a detailed view. Clicking the same button again restores the full grid.