Hi Guenter,

Thanks for your letter.

> after a long time of rest I have again reached a point

> were I have to cry for help.

Sorry you are having trouble getting your bitmap to align with the plot. These tools are pretty complicated and take a bit of practice to get them to work right.

> The main problem/wish is to have a fixed topografic bitmap

> which fits my cave, so no further zooming is necessary,

> adjusting manually the position is ok, but I want to have a

> bitmap, which fits my cave, if I use the scale of 100

> Meter/cm, so that I don't have to rezoom it again and again.

The scaling values that are contained in bitmap images are very seldom accurate. On the other hand, the cave survey is generally much more accurate since it is made up of dozens of hand measurements. For that reason, Compass ignores the scale values you find inside a bitmap. As a result, the process of matching a cave to a bitmap is done by re-scaling the image, not the cave. When you set the cave's scaling to 100 Meters/cm your are only setting it for the purpose of printing or display. It does not have an effect on matching the cave to a bitmap.

> First: Whenever I lock a bitmap, the bitmap shrinks on the

> screen, where is the switch to stop that shrinking?

Again, Compass adjusts the bitmap to fit the cave, not the other way around. The bitmap shrinks because you have already zoomed the cave to a different size/scale. When you enable the "Lock-Image-To-Cave" option, the program realizes that you have changed the size of the cave and it resizes the bitmap to match.

> Second: With my cave at a scale of 100 Meter/cm I tried to

> prepare a topografic bitmap, which fits. But it does not. I

> think, that some/thing/one changes the DPI or whatever. What

> are the real conversion figures to adapt my bitmap? My

> topografic bitmap has 4000*3000 pixel at 72ppi (28,346 pixel/cm).

> 4000 pixel equals 5 km in nature. (At least this is what I can see in

> Photoshop)

The values you see in Photoshop may not even be included in the bitmap and so Compass does not even attempt to use them.

Here are the steps you need to take to adjust a bitmap to match your cave.

1. Load the cave data into the Compass Viewer. Don't worry about the cave scale factor at this point.

2. Load the bitmap into the Viewer using the "File -> Load Bitmap" option from the Menu Bar.

3. Select the "File -> Adjust Bitmap" option from the Menu Bar.

4. Immediately turn on the "Lock-Image-To-Cave" option.

5. Now use the "Move Bitmap" buttons to move the Bitmap so the location of the entrance matches the entrance on the plot of the cave.

6. Now adjust the Scale so the bitmap is the proper size for the cave. This is hardest part. I usually try to find something on the bitmap that is of a known size. For example, if it a topographic map, you can usually find grid lines, a length of road, a lake or just any two land marks. If you measure their distance on the topographic map, you will know how long they should be in relation to the cave. Once you have identified an object of a known size, select the "Tools -> Measure Distance/Angles" option in Compass. This will allow you to measure the size of the object on the bitmap. If the object measures too big or too small, adjust the Bitmap Scale in the "Adjust Bitmap Background" window. Keep re-measuring and adjusting until the error is very small.

7. Final step is to adjust the rotation. If you have used the proper Declination on all your survey files, the cave should be aligned to True North. If the bitmap is also aligned to True North, then you won't have to do any rotating. However, if the cave does not have any declinations and the cave plot will be aligned to magnetic north and so you may have to rotate the bitmap. Likewise, many bitmap images are not aligned to True north. If that is the case, then you will also have to do some rotating.

In all this process, you can use the regular Pan, Zoom and Rotate options in Compass to position the cave and the bitmap where you want. Since you have locked the cave and the bitmap together, changing the overall rotation, pan and zoom position won’t affect the relative position of the cave and bitmap.

8. Once the Bitmap and the Cave have been adjusted to match each other, you can now close all the "Tool" windows and navigate as would normally do in Compass. You can zoom, pan and rotate, and the cave and bitmap image will track each other. You can now set the overall Scale to any value you want (including 100 meters/cm) and the cave and bitmap will print at that scale. The value is set using the "Action -> Scale, Magnification, Rotation" option from the menu bar.

There are couple caveats with this process:

First, very large bitmaps may be slow to update, particularly when you do any rotations. This is dependent on the kind of computer you have and the graphic card drivers. Your bitmap is 3000x4000, which is pretty large. If the update rate is intolerably long, Compass offers you the option of reducing the image size. Even a small reduction in size can speed things up a lot. For example, cutting the size in half will increase the speed by four times.

Second, there is a bug in the rotation routines that sometimes causes shifts in the position of the cave relative to the bitmap. It only happens under certain circumstance and I haven't' had time to track down the problem. (Besides, I may just shift over to using OpenGL, which may be a better solution.) In any case, be aware of the problem. You can usually avoid it if you don't rotate the cave.

> Btw. the Image Position shows always only the indication

> "Ft." not "M.", but it really changes the values to Meter or

> Feet.

Yes, thank you. It is a bug and I have just fixed it. There is a new version of Compass on the Internet with the problem fixed.

Thanks again for your letter. I hope it helps you solve the problem.

Larry