Importing surveys with no data

[Wookey]

+++ Stacho Mudrak [04-12-29 09:44 +0100]:

>>> >I am wondering if there is a better way - so I put the drawings in and say
>>> >'these are all we have - you work it out', rather than using
>>> >ill-defined stations which were only made up by taking off this very
>>> >same drawing in the first place but now they have been through numerous
>>> >innacuracies and distortions.
>
>>
>> There two possibilities how to solve this:
>>
>> 1. To position each scrap - in principle you need only two stations for
>> each scrap. You do not need to enter a lot of stations. Then in output
>> you can hide those virtual stations using symbol-hide group centerline.


Yes I've been doing this - and since discovering debug mode I've been
correcting the stations which were badly placed. Nevertheless there seem to
be some errors in our original 're-generation' of the fake data which means
there is some stretching of of the image. It would be better to use the
image itself as the reference, with the only stations involved being ones
where real surveys connect.

I tried adding one passage (for which we didn't even have 'fake' data) as
'projection none', but this just produced an error (something like
'incompatible projection'). Is it possible to mix projection none and plan
in a map (and have joins between them)? If not how would you add a load of
old 'lost data' survey to some new data (which is what I need to do).

>> 2. You can use projection none for that - but then you will need to
>> calibrate each scrap at real coordinates (if you have some grid on your
>> paper, this should not be a big problem).


I don't have a grid on the paper. There is nothing but a scale bar in one
corner. What exactly am I trying to do here? There are 8 number to be given
- 4 picture scale points and 4 real scale points. Let us say I have a scrap
on a sheet of paper and I know nothing but the distance that corresponds to
50m. How might I go about making up some numbers for the scrap?

And would I then just copy those numbers to all the other scraps?

I suspect we need a little how-to for importing such 'lost data' surveys to
therion, and how to best combine them with new survey data.

>> 3. We can change the behaviour of therion and allow calibration of
>> scraps using only -scale option also in other projections (currently it
>> is allowed only in the "none" projection) But in any case, you will need
>> to specify -scale for each scrap.


Would this solve the 'incompatible projection' problem when connecting to
plan projection scraps?

>> In the scrap -scale option, you can specify coordinates of two real and
>> corresponding two image points. There is no scalebar or something like
>> that. Copying can be done in text editor (very carefully  :)


OK - but as above I have no idea how to give these numbers. Which way do
they increase? are both sets of numbers entirely arbtrary and only the ratio
matters? Are there overflow limits I should worry about? and so on...

What a lot of questions!

Wookey
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