[Therion] Bitmap calibration

[Bruce Mutton]

Mara
Attached is an example of my use of a surface bitmap.  Only the top three
lines of the surface definition are required, the terrain model is optional.

>I need to insert data of 2 different points, so entrance of the cave 
>is 0 0 and I can get the relevant bitmap pixels data from a software 
>like Microsoft Paint. 

Yes, although it is probably easier to use real world co-ordinates, say from
a topographical map. (You will need to invoke the co-ord system in the
survey files and the thconfig file as well - the syntax is the same as in
the attached.  Make sure you use a locally relevant system - the one in my
file will only give you a sensible result if your cave is located in a
particular region of the south pacific.  And further, you can use different
co-ord systems (but not arbitrary cave centred ones) for your inputs and
outputs, so long as they are all locally relevant - Therion will convert one
to the other quite happily)

>Now, the question is how should I get the data for the second point? I 
>have no knowledge of where the stations are compared to the surface.

Precise knowledge of where the cave stations are is not required.  Therion
will sort it out provided you fix the entrance with the correct real world
co-ordinate.  For a sensible output this would be somewhere generally
between the image corner co-ords.  For example I have used the bottom left
pixel and top right pixels of the example image, as I know their real world
co-ordinates.

>And also, to make sure the scale is correct I should just export tha 
>map with same scale as the surface map scanned, is this correct or I am 
>missing something?
Not relevant, as the above process will morph the map to the correct
orientation and scale regardless of the scan resolution.

>thanks a lot for yr help
Yr welcome

Bruce

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