[Qgis-user] Aligning georeferenced USGS historical map

[Andreas Plesch]

Looking at

https://ngmdb.usgs.gov/img4/ht_icons/Browse/CA/CA_Tamalpais_301790_1897_62500.jpg

there is a note in the lower right corner:

Polyconic projection. To place on North American datum, move projection
lines 690 ft south and 320 ft west.

https://en.m.wikipedia.org/wiki/American_polyconic_projection

explains the projection.

Unfortunately, the map does not mention which central meridian was chosen
for the projection. It may be possible to find if at the time a single one
was used for all of CA and what it would be.

It should also be straightforward to determine if proj  and therefore qgis
supports the polyconic projection. It probably does.

With that you can define a custom projection. Perhaps there is an EPSG code
but I could not find it.

EPSG 9818 seems to encode this projection although it does not seem to
include the actual method in the registration.

After you have defined a closely matching projection, you can translate the
minute grid points to projected coordinates and georeference.

The other mystery is the note about the datum shift. What are projection
lines and what datum is used for the printed map ? The mentioned North
American datum may be NAD27.

Andreas


From: Morgan Fletcher <morgan at hahaha.org>

> To: qgis-user at lists.osgeo.org
> Subject: [Qgis-user] Aligning georeferenced USGS historical maps
> Message-ID:
>         <
> CAPwdt1U+TmE7cJR4GF63E13MPaPYWO9nsbzocHj2R8nG80duhw at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> I am new to GIS, an amateur who is curious about old roads. I have QGIS
> 3.4.0 installed on OS-X 10.13.6 using the pre-built binaries available from
> https://download.qgis.org/. If I visit the USGS topoView
> <https://ngmdb.usgs.gov/topoview/> page and download a historic map, for
> instance the geotiff archive from Tamalpais, CA 1897 (1950 ed.)
> <https://ngmdb.usgs.gov/topoview/viewer/#10/37.8564/-122.6336>, I can add
> a
> raster layer with the .tif file from the archive and it will be placed in
> rough correspondence with a base map in my QGIS project. In my case my
> basemap is OpenStreetMap. (crs=EPSG:3857&format&type=xyz&url=
> http://a.tile.openstreetmap.org/%7Bz%7D/%7Bx%7D/%7By%7D.png&zmax=19&zmin=0
> )
> The problem is that the maps don't line up, visually. For example:
>
>
>  Screen Shot 2018-11-02 at 8.51.02 AM.png
> <
> https://drive.google.com/a/hahaha.org/file/d/0B-OybZpGWIkHUWhuWEZLS2xWZEhTUC1MMkN4X2dfZGkxQm1J/view?usp=drive_web
> >
>
>
> I can solve it better with georeferencer. Before I viewed Hans van der
> Kwast's excellent Georeferencing a scanned map and digitizing vectors in
> QGIS <https://youtu.be/4IWyVeGhzog> video, I simply started finding common
> points; now I understand that using the correct CRS, projection and the
> grid is perhaps perhaps the best strategy.
>
> My questions are:
>
>
>    - If I download a geotiff archive from topoView, is QGIS 3.4.0 correctly
>    parsing the data in the .tif file, or the other files (.prj, .tfw) in
> the
>    extracted directory, and placing the map correctly? Can it be adjusted
> to
>    align better, and if so, how?
>    - Should I use EPSG:26710 for the Tamalpais
>    <https://ngmdb.usgs.gov/topoview/viewer/#10/37.8754/-122.6260> map, and
>    attempt to georeference it myself, using its minute grid? Why does the
> map
>    border show a skew at the top left and right corners? (see below)
>    - I have found that, to get a hand-drawn, antique map to align with a
>    modern base map, I often have to add so many points in georeferencer
> that
>    the rendered map has to be very distorted. What is the best method to
> get
>    old maps to line up, so that historical roads can be related to modern
>    roads?
>
> Skew mentioned in second point:
>
>
>  Screen Shot 2018-11-08 at 8.20.56 AM.png
> <
> https://drive.google.com/a/hahaha.org/file/d/0B-OybZpGWIkHeEE0aDMyQVFCZ0F1R01pRGhKeEJVTzYxaEpj/view?usp=drive_web
> >
>
>
> I couldn't find a searchable archive of qgis-user; my apologies if these
> are already answered somewhere. I did ask a variation of these questions on
> StackExchange
> <https://gis.stackexchange.com/questions/301199/fix-offset-of-geotiff-file
> >,
> where it was heavily edited by 'Vince', and has no answers after a week, so
> asking here.
>
> Morgan
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