Image - Download

The Download command appears when the focus is on a window for an image linked from an external image server such as an OGC WMS image server, a Microsoft TerraServer image server or a Manifold Image Server compatible third party module such as Google. The command allows automatic download of all tiles available for the image at any level of resolution available. Tiles will be assembled into a single image at each resolution level selected.

 

Note that before the Download command appears, we must have already used File - Image - Link to create a linked image from an image server such as TerraServer or an OGC WMS server. The maximum detail available in the downloaded image will have been set by the choices made when initially linking the image, such as the use of the Min Scale parameter in the TerraServer dialog or the Size parameters in the OGC WMS dialog.

 

images\btn_chkbox_sel_all.gif

Select All - Check all the boxes in the levels pane.

images\btn_chkbox_sel_none.gif

Select None - Uncheck all the boxes in the levels pane.

images\btn_chkbox_sel_inverse.gif

Select Inverse - Check all unchecked boxes and uncheck all checked boxes in the levels pane.

(levels pane)

Check levels to be downloaded. The Level column reports the resolution in pixels at each level. The Tiles column reports the total number of tiles as well as the approximate number of tiles already linked at each level and thus available from cache, if caching is on (the default) for faster download.

(status bar)

The number of tiles to be downloaded of the total number of tiles available with the current set of levels checked. The number to be downloaded is in addition to those already in cache and so provides a useful guide when the connection to the image server is slow.

 

The image download process will run in background to allow other work to proceed while the image is downloaded. Take care not to capriciously select very detailed levels for download if your connection to the image server is very slow. Downloading levels of an image linked from a remote image server proceeds from the least detailed levels to most detailed levels. This provides a reasonable chance of getting at least some useful, complete levels in case a connection is interrupted.

 

Images may be downloaded at a variety of detail levels. The most detailed level that may be downloaded will be set by the parameters specified when linking the image (Min scale in the case of TerraServer images and Image size in the case of OGC WMS images). The least detailed level will be set by the least detailed data level available on the server. The Download dialog allows us to choose which level of detail we want between the most detailed and the least detailed available and to download the resulting image into a local image so that subsequent work with the image is faster or more convenient.

 

For example, we could use the Download dialog to fetch a complete image from the server so we can later work with that image when disconnected from the server. We might also use the Download dialog to download all tiles in the most detailed image level prior to exporting the image to a local file, perhaps as an ECW image.

 

Image - Download and Image - Relink / Unlink Compared

 

An image linked from an image server may be converted to a local image within the project either by using the Image - Unlink command or the Image - Download command. The Unlink command converts the existing linked image to a local image at whatever resolution is currently in use. The Download command may be used to automatically fetch all image tiles at any available resolution to create a local image at that resolution.

 

Images linked from external servers normally may also be exported to image files. In that case, the exported image will be the same as that which would be obtained by unlinking the linked image.

 

Note that exporting or unlinking an image linked from an image server will only use the data already downloaded from the server and will not attempt to download any more data. It will also only use the data for the most detailed image level. It is usually a good idea to use Image - Download to check how much data has already been downloaded for the most detailed image level prior to exporting or unlinking the image.

 

Another way to create a local image from a linked image is to open the linked image and then to use the keyboard F6 command or the Tools - Make Image command. The Make Image dialog allows us to create a local image in several different ways from the linked image without unlinking the linked image. For example, we can use this command to create an image of the displayed window or of the entire linked image at a desired number of pixels or scale.

 

Very Important

 

Before using Export with an image linked from an image server, see the Very Important discussion in the Image - Unlink command.

 

See Also

 

Linked Images from Google Servers

Linked Images from Manifold Image Servers

Linked Images from OGC WMS Servers

Linked Images from TerraServer

Image - Relink / Unlink

Tools - Make Image