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 Projections and datum
 NAD27 (Clarke/1866) Not Avaiable.
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Lost Adams

USA
4 Posts

Posted - 24/10/2012 :  23:52:31  Show Profile  Reply with Quote
I am trying to georeference a 1922 30'x30' Geologic Map.
I can't find the NAD27(Clarke/1866) DATUM in the list.
In QGis the avaiable options are NAD27(Western/US) but it doesn't work eihter, makes the map square not rectangular.
I get a 299dpi in the info panel.
When I use the default value of WGS84 in OKMap I measure the 6mi long scale on the map as 7.2mi.
I have tried to rescale/georef the map but the Scale dropdown menu remains grayed out.
What my intended use is to be able to use OLD Geologic Survey Maps to make newer maps that I can use for Gold Prospecting.
Sincerely
Bill Adams

okmap

Italy
2355 Posts

Posted - 25/10/2012 :  19:24:24  Show Profile  Visit okmap's Homepage  Reply with Quote
The datum you are searching is named "NAD27 (NADCON)" in OkMap.
Is it possible that you are searching in the list of "Predefined projection" instead in datum list?
What do you intend for rescale map? Resize function in Utility - Map tiling?
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Lost Adams

USA
4 Posts

Posted - 26/10/2012 :  02:17:49  Show Profile  Reply with Quote
I want to take a tiff image file and georeference it.
The file is of an old USGS Geologic Map for the Riddle Quad 1/125000 from 1923. URL: http://pubs.er.usgs.gov/publication/gf218
it is the "Plate 1" map in pdf format. I loaded the pdf in Acrobat Reader and Saved it as a *.tiff file as the same name.
What I want to do is load the GeoReferenced tiff into OKMaps and/or QGis and Trace the polygons of the Rock Formations to a new Vector layer. Then save that layer to a *.shp file to be overlayed in a newer Larger Scale 1:24,000 or 1:12,000 map for my field work. This new map will have 8 vector layers of
colored Geologic unit Ploygons,
DEM Contours,
Roads,
Topo Labels,
Geologic unit Labels,
Rock Contacts, and
Faults.
This information will come from the work done by the USGS in the late 1800's and early 1900's maps.
The NEWER Maps have almost all the Mines and Cabins and Trails REMOVED from them.
I also will use this info to help in Finding Lost Gold Mines and Other Lost Treasure's.
Sincerely
Bill Adams
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okmap

Italy
2355 Posts

Posted - 26/10/2012 :  10:19:03  Show Profile  Visit okmap's Homepage  Reply with Quote
if you save a pdf into a tiff file you'll obtain a tiff (not a geoTiff) so this file it isn't georeferenced.
You'll procede to a manual calibration with OkMap.
After having calibrate you can load Esri shape file over the raster map and then save the map image as a new tiff file (if you want obtain a raster merge with tiff image and vectorial data).
To calibrate the raster map you should set the map datum to "NAD27 (NADCON)" and the proper projection. Then set the grid setup copying the map datum/projection.
After draw at least 3-4 calibration point using (if possible) the grid drawn on the map.
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Lost Adams

USA
4 Posts

Posted - 26/10/2012 :  22:56:33  Show Profile  Reply with Quote
Thank You for your help! I think I understand what the "workflow" is with your software now.

Sincerely
Bill Adams
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