Importing surveys with no data

[Stacho Mudrak]

> 'incompatible projection'). Is it possible to mix projection none and plan
> in a map (and have joins between them)?


No it is not. In the map - all scraps have to be from same projection.

> If not how would you add a load of
> old 'lost data' survey to some new data (which is what I need to do).


Well, If I should do this, I would probably do it following way:

1. For each paper define one virtual station, that will position this paper in real world coordinates.

2. For all scraps on this paper, I would insert into each of them only this single station (and I would give it -visibility off option, that it will not be visible in the map).

3. Scaling and rotation of scrap would be done using -scale option. If you have a horizontal 50 m scalebar on the paper, and paper is facing north, than I would use 0 0 50 0 as real scale coordinates for edges of scalebar. See attached picture. Real coordinates are not important, only their difference (vector) is. Scrap will be positioned according to stations specified in it.

> - 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?


As above. All you need to do is to specify paper and real vector. From these two vectors rotation and scaling are determined.

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


Yes, for all scraps lying on the same paper, these numbers would be same.

> 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...


Both paper and real coordinates are standard cartesian. X = east, Y = north. Yes, numbers are arbitrary, important are only relative positions. There are no overflow limits - you can probably use any numbers you like.

4. When scraps will be drawn, I would then adjust positions of those virtual paper stations, that scraps will be as close as possible. When scraps will be close to each other - then I would join them. And that's all. You will need only so as many stations, as many papers you have.

Mixing projections, or calibrating scraps only using scale option I do not consider as a good idea. Once you may decide to use other coordinets (e.g. GPS), and you will need to shift all papers somewhere else. If real coordinats will be in form:

fix paper1 10 20 30
fix paper2 20 30 40

it will be very simple, because it will be in one table. If scaling points would be in scrap headers, it would be very hard.

Another point - this way (one station per scrap or paper) each scrap also receives some vertical information. If you would like to color scraps according to altitudes (it should be possible in the next release), it will be also possible. When scaling scraps only using -scale option, there is no vertical information.

I am not sure, whether I wrote it understandable way, but I hope you understand what I wanted to say.

Happy new year to everybody,
S.