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Importing Sketch-maps.

IV. Importing Sketch-maps. Most people derive the passage walls in their finished maps by tracing the scanned versions of the sketch-maps for the cave. This section will show  you how to trace sketch-maps in Inkscape. (If you don't have sketch-maps, you can use the passage-wall information from the plot file to trace the passage walls. Click here for more information.)

To trace a sketch-map into Inkscape, you need a scanned image of your sketch-map. It is also very useful to process the sketch-map through the "Compass Sketch-map Editor" before you trace it in Inkscape.


In this tutorial, we will use a sketch-map of the B-Survey from Fulford Cave as the example. The sketch image has been processed with the Compass Sketch-map Editor to combine and align six sketch-maps into a single image.

This makes it easier to trace because you can work with a single image instead of six separate pieces. It is also more accurate because the bitmap has been warped so that it perfectly matches the survey data.

A. Loading A Sketch-map. The first step in the process is to load the sketch-map into Inkscape. Be sure that one of the "cmp_Sketchmap" layers has been selected and enabled before you start. (You can use either layer for your sketch maps and you can add more more layers if you need them.)


To load a sketch map, go to the "File" menu and select the "Import" option. This will allow you to open any common type of bitmap image.

B. Preparing The Image. When the image is loaded, it will appear in the middle of the Inkscape screen. The first task will be to scale and position the image to match the scale of the plot in Inkscape.

You will probably want to zoom in a bit so you can see survey stations and the shot lines. You can do this using the magnifier tool in the bottom-right corner of the Inkscape Window.

C. Scaling The Image. The main goal now is to scale and position the sketch map image so it matches the scale and position of the survey lines and station locations in the SVG file that was exported from Compass.
 Start by making sure the "Selection Tool" button is down on the left-hand tool bar.

Next, make sure the "cmp_Sketchmap" layer where you loaded your sketch map is visible, unlocked and  selected. in the Layer List on the right. That will select the proper layer.

The final step is to select the individual object in the layer. Right now we only have one sketch map loaded, but in the future, we may have more than one, so the next step is important. Just click on the sketch-map image in the main window to be sure it is selected.

This will cause the Image-Size control to appear on the tool bar at the top of the window. You want to maintain the aspect ratio of the image as we scale it, so press  the "Lock" button between the W and H boxes.

This locks the two controls together so the aspect ratio of Width to the Height is maintained constant no matter what size the image is set to be.

Now start changing the Width or Height of the image. Both dimensions will change and the image's size will change along with it. The goal is to adjust the sketch map so the stations and shot lines in the sketch match of the line plot. You do this incrementally, so the first time, just try to get it close. We will fine tune later.

D. Repositioning. As the size changes, you will need to reposition the image. You can do this with the Image Position controls on the top tool bar. The "X" control moves the image right and left, and the "Y" control moves the image up and down.

 

You can also move the image by clicking on it and dragging. (If you have any problems, make sure that the image and the proper layer are selected.)

E. Fine Tuning. At this point, you are trying to get all the survey stations in the sketch to exactly match the position in plots. Since it is easy to over shoot in your adjustments,  I usually work on one end of the sketch and then on the other, making small adjustments. As you do this, the errors will get smaller and smaller. If you prepped the images using the Sketch-Map Editor, you should be able to get all the stations right on target.

The example on the right shows the sketch map close to the final position, but not quite there.  The sketch needs to be moved slightly down and to the right so the station markers at B1, B2 and B2A are align perfectly the sketch map.

To make the process easier, the closer you get having things properly aligned, the more you want to zoom.

When you are satisfied with the position and the scaling, lock the layer so you don't accidentally move it.

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