Before we start getting into the preparation of data, let´s first get out of the way a common misunderstanding: Shape is not a software that processes observational data and as a result delivers a 3-D model. 

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What Shape does is to provide you with a set of tools that allow you to apply your scientific insight and creativity to generate a 3-D model that reproduces your data as closely as possible. During this process you might improve your understanding of the object of your research and with the final model you have a tool to help your peers to better understand your conclusions.

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Selected Window:

Data as a reference in the Render Module are included per Window,  which may be an Image or a Position-Velocity (P-V) window. Clicking on a Window selects that window, which is indicated by a thicker white border of the window. 

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Once a window has been selected, the drop-down list at the top of the Properties tab gives access to the selected window by chosing Selected Window.

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Two important choices to be made at the top are the flags Render and Master. By default all windows get rendered, but sometimes it may be prefereable to not render some windows. 

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Only one of the windows can have the Master switch on. Once you select Master for a window, the corresponding switch in the previous Master window is switched off. 

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The Master switch determines which rendered or reference image can be shown in the Render View of the 3-D Module as a reference background during the modelling process. 

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The potential of cross-checks between data and models:

 

It has happened in several occasions that the model result hinted at problems with the data processing and resulted in the correction of mistakes. Hence, frequent critical cross-check between data and model can be beneficial in both directions. Usually the data inform the modeling process. Occasionally it also happen that the modelling leads to corrections, new processing or interpretations of the data. 

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Data Preparation:

Data for Shape basically consist of some form of image that is placed as a reference in the background of the rendered images, spectral images or the 3-D views in the 3-D Module. Shape provides tools to correctly place the images in their corresponding context. 

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The key information that is needed to prepare these images are their scaling and corner positions in the chosen coordinates. 

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So, for instance, if you wish to work on arcsecond scales and your side to side field of view is 10 arcsec, then you have two options. First, you crop your image to the same field of view. Then, after loading it into Shape, it fits automatically to the 10x10 arcsec field that you have set up. This is the recommendable option.

 

The second, more complex, but often necessary option is to use a certain image as it is. Then the position, rotation and size are adjusted in Shape such that it is correctly placed in the field of view.

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These options are applicable for images, P-V diagramas, channel maps and graphs.  

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If your images have scales with tick-marks, you can adjust the placement such that they coincide with the corresponding tick marks in the Shape image coordinate system. This can be done in position and velocity.

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In the first example on the right (click on the image to see a larger version) the observed image was first cropped to a square format that corresponded precisely to the original size of the default window size or range values. 

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As long as no rendering was done, the background image remains visible. The visibility of the background image is indicated by the red square in the top-left corner. Once your models become very realistic you may not immediately notice whether you are looking at the observed or rendered image. Then it may happen that you are wondering why your rendering hasn´t changed after your changes in the 3-D model settings... until you notice that there is a little red square that tells you that you have been staring at the observed image all the time. 

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To gradually switch between reference and rendered image use the Transparency slider.

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In the second example on the right, a new P-V Window was added. A single position velocity diagram as shown further up was added as a background. The x0, y0, x1, y1 values were adjusted such that the image fits precisely in such a way that the tick marks in the observed image and render window overlay correctly. A small additional correction was applied by adding a Translation Modifier to the observed image with an adjustment in the x-direction. Other modifiers can be added to correct scaling and rotation of the reference image. Note that the order of the modifiers in the stack may be important, especially when there are rotation and translations combined.

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Rendered images as references for changes:

Often one needs to compare a previous rendering with the one that includes new changes to the model. Rendered images can be saved as reference images after you open the background Image drop-down list and select None. Then click on Save image. A new item in the image stack appears labeled with the time the image was saved. A whole sequence of rendered reference images can be build by repeating this process. To delete an image from the stack, select the image and press Remove image.

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