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 Projections and datum
 RT90 projection Sweden, calibration error
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okmap

Italy
2310 Posts

Posted - 26/03/2012 :  12:28:26  Show Profile  Visit okmap's Homepage  Reply with Quote
OkMap don't read zip file.
I tell you to use zipped file to upload to the forum.
Modify directly the file:
C:\Documents and Settings\<user>\Dati applicazioni\GianPaoloSaliola\OkMap\<version>\defs\datum.xml
Try to remove Bursa-Wolf parameters and retry to georeference your map. Tell me if this correct the issue.
However send me your map at mailto:info@okmap.org so I'll do some tests.
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okmap

Italy
2310 Posts

Posted - 28/03/2012 :  08:51:15  Show Profile  Visit okmap's Homepage  Reply with Quote
Hi Peter, I've received your map by email.
I've only changed the predefined projection to "RT90 0 gon" and nothing more.
Your georef points was good.
Now calibration seem ok.
1. Grid match on map very good
2. If you launch Utilities - Goole Earth (map + gpx) maps overlay perfectly with background (use transparency slider to check the goodness of overlapping).
This is the new .okm file:

Allegato : 6B_13.zip#9;1.32 KB
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PeterHe

Sweden
10 Posts

Posted - 03/04/2012 :  13:21:19  Show Profile  Reply with Quote
Hi again,

Many thanks for your verification, I am really grateful for your efforts. I have now also found the actual problem: I thought alternative grid over-rode the map setup, but it didn't (I compared your map-file and mine - the projection was incorrect in mine).

The whole reason for the problem is the (what I find) somewhat confusing input dialogue, the principal steps are however easy to understand. I believe it would be much easier to always select datum/reference, projection and grid, using {\em identical} terminology everywhere. For instance change the two "map setup" and "grid setup" to three: "Datum setup", "Projection setup", "Grid setup", with a "help" containing brief information below all three. The datum or reference is then the reference information for what is the origin, rotations and the model shape of the earth. The projection describes how to flatten it out to print it on a planar surface. The grid is just the guiding lines on the map. Now, the datum and/or projection is selected in different places in a non-uniform way but with very similar names all containing RT90, RT90 0 Gon and RT90 2.5 Gon V. In the map-file I can find both RT90 O Gon as well as RT90 2.5 Gon V, which appears contradictory. Geographically, it appears I should use RT90 5 Gon V or perhaps RT90 7.5 Gon V - but that is only used for large scale maps.

Would it be possible to rearrange the input dialogue to be more 'logical'? At least make the alt grid option inactive as long as no alt grid has been selected (and some information how to do it...)? Sorry for all opinions but the handling is really important to avoid mistakes. I also understand that the standards for maps are mixed and confusing so it is not simple to construct the input dialogue.

Thanks again for an overall excellent program, I will make a donation shortly.


Best regards,
Peter
(Sorry for not responding earlier but I have been away for a few days...)




quote:
Originally posted by okmap

Hi Peter, I've received your map by email.
I've only changed the predefined projection to "RT90 0 gon" and nothing more.
Your georef points was good.
Now calibration seem ok.
1. Grid match on map very good
2. If you launch Utilities - Goole Earth (map + gpx) maps overlay perfectly with background (use transparency slider to check the goodness of overlapping).
This is the new .okm file:

Allegato : 6B_13.zip#9;1.32 KB

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okmap

Italy
2310 Posts

Posted - 03/04/2012 :  15:17:35  Show Profile  Visit okmap's Homepage  Reply with Quote
Peter, about projection name I've used official names of GeoRepository database (see at http://georepository.com/search/by-name/?query=sweden&include_world=on and click on "Projections (6)" tab).
OkMap has 2 setup buttons named "Map setup" and "Grid setup".
The first setups map datum and map projection through a wizard.
The first form of the wizard lists all known "predefined projection" (they are a combination of datum+projection). If you find your combination the wizard ends. If not, select "Customized projection" and the wizard continues with a datum selection and then with a projection selection.
This may be sufficient to calibrate a map.
The second button (grid setup) is to specify the datum and projection used to draw the metric grid on the map (normally it's the same of the map but I've encountered some russian maps where those was different). The "Grid setup" button also enables the "Alt" grid tab in the box coordinates so, if you want that OkMap draw the alternative (metric) grid or you want to use the "Alt" tab, you should copy (normally) the alternative grid same as map projection (there is a button to do this). I hope that this clears a complicated issue.
I apologize for my brutal English .
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