Map Gridlines

The Map Gridlines tool creates a map gridlines (graticules) layer which includes coordinates labels and an image border. Layers -> Map Gridlines Toolbar: Layers

*Note: this help page is slightly out of date - see SeaDAS 7.4 Release Notes

Map Gridlines have been significantly revised for SeaDAS 7.1 with a lot of new parameter option choices for the user. Below are some examples.

The following 4 images were created with SeaDAS using the same Chloryphyll product scene of a level-2 file. They show various applications of map gridlines along with the effects of reprojection on the map gridlines.

Image 1 shows map gridlines on an image of standard l2-file Image 2 shows map gridlines on a reprojection of the same file as Image 1 Image 3 shows another variant of Image 2, but with labels placed inside the image Image 4 shows another variant of Image 1, but with only corner labels

Editing parameters of the map gridlines - To edit any of the parameters click on the Layer Editors icon . This will enable you to edit whichever layer is currently selected. If the Map Gridline layer does not show up in the Layer Editors window, then toggle the Map Gridlines button off then on, this will make the Map Gridline layer the selected layer. The Layer Manager window is another place where you may select a layer to be the selected layer.

The following image shows the user editable components of the map gridlines. Most fields are pretty self-explanatory.

Gridline Spacing - The latitude and longitude step sizes may be set directly where the value represent degrees between the gridlines. Setting this field to zero results in Auto-Sizing. The Auto-Sizing algorithm will set the gridline spacing to a reasonable value such that there are about 3-5 lines. Also note that lines are placed at the nearest most sensible degree value.

Font Sizing - The user font settings are in term of points rather than pixels. This enables a single user font setting and default to work well with files of any resolution. Internally the font sizes are actually tied to the pixel sizes and there is a conversion of points to pixels being made.

Low Resolution (in pixel space) Problems - For files with an extremely low resolution image, less than about (100 x 100) pixels resolution, you may expect to see problems with the map gridlines, such as missing labels.

Put Labels on Inside - By default this checkbox is unchecked and the coordinate text labels are placed outside the image. This looks great and is our preferred look. But, keep in mind, that when an image window is first opened, the image fills the window (at least in one dimension). Toggling the gridline labels on and off doesn't affect the zoom of the image. So to view these "outside" labels, the user will need to zoom the image out.

Exporting an image with gridlines - Use the "Export Image" tool. This tool is located at File -> Export Utilities -> Image or it can be found in the drop down menu when the image is right clicked with the mouse. If your labels are "outside" the image then select "View Window" from the "Source Boundaries" panel. For more on this see Publication Quality Images.

User Preferences - For this release most of the preferences have been removed, but decent automated defaults are being used which are dynamic to the image resolution. We do plan on updating the user preferences capabilities to include all the new options in a future release.