<div dir="ltr"><div class="gmail_quote"><div dir="ltr"><div class="gmail_quote"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div>It looks like the GeoTIFF at <a href="https://ngmdb.usgs.gov/ht-bin/tv_download.pl?id=5504707&tif=true" target="_blank">https://ngmdb.usgs.gov/ht-bin/tv_download.pl?id=5504707&tif=true</a></div><div><br></div><div>actually uses an (almost) correct projection:</div><div><br></div><div> <span style="color:rgb(0,0,0);font-family:monospace">PROJCS["Polyconic",GEOGCS["GCS_North_American_1927",DATUM["D_North_American_1927",SPHEROID["Clarke_1866",6378206.4,294.9786982]],PRIMEM["Greenwi </span></div><span style="font-family:monospace">ch",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Polyconic"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-122.625],PAR
<br>AMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["Meter",1]]<br></span><div dir="ltr"><br></div><div>and proj knows about polyconic:</div><div dir="ltr"><br></div><div dir="ltr"><a href="https://proj4.org/operations/projections/poly.html" target="_blank">https://proj4.org/operations/projections/poly.html</a><br></div><div dir="ltr"><br></div><div>Since the geoTIFF projection mentions NAD 1927, perhaps the main issue the datum shift mentioned on the map.</div><div><br></div><div>So I tried to find out about the datum actually used for the printed map and found this:</div><div><br></div><div><a href="https://historicalcharts.noaa.gov/links.html" target="_blank">https://historicalcharts.noaa.gov/links.html</a><br></div><div><br></div><div>linking to</div><div><br></div><div><a href="https://historicalcharts.noaa.gov/pdfs/AR1853_Appendix39.pdf" target="_blank">https://historicalcharts.noaa.gov/pdfs/AR1853_Appendix39.pdf</a><br></div><div><br></div><div>Page 101 has a table of constant used for the polyconic projection including the ellipsoid parameters (older than Clarke 1866).</div><div><br></div><div>With that a new custom projection can be defined:</div><div><br></div><div><p style="margin:0px;white-space:pre-wrap">+proj=poly +lat_0=0 +lon_0=-122.625 +x_0=0 +y_0=0 +a=6377397.16 +b=6356078.96 +units=m +no_defs</p><p style="margin:0px;white-space:pre-wrap"><br></p><p style="margin:0px;white-space:pre-wrap">and assigned to the geoTIFF (without warping), replacing the NAD27 datum definition.</p><p style="margin:0px;white-space:pre-wrap"><br></p><p style="margin:0px;white-space:pre-wrap">Interestingly, this change shifts the map ca. 690ft north, and makes it align better but not perfectly with modern maps. The purple tinted map below is using the new custom projection, using on the on the fly reprojection which may not be accurate enough.</p><p style="margin:0px;white-space:pre-wrap"><br></p><div><div class="gmail_chip gmail_drive_chip" style="width:396px;height:18px;max-height:18px;background-color:rgb(245,245,245);padding:5px;font-family:arial;font-weight:bold;font-size:13px;border:1px solid rgb(221,221,221);line-height:1"><a href="https://drive.google.com/file/d/0BwIhFzkLaQ9Xd1pPd1FNTHM5WWplQTZVcHJ0S2pOUFFPM3Fz/view?usp=drive_web" target="_blank" style="display:inline-block;max-width:366px;overflow:hidden;text-overflow:ellipsis;white-space:nowrap;text-decoration-line:none;padding:1px 0px;border:none"><img style="vertical-align: bottom; border: none;" src="https://drive-thirdparty.googleusercontent.com/16/type/image/png"> <span dir="ltr" style="vertical-align:bottom">image.png</span></a></div><br></div></div><div><br></div><div>I think the dotted lines at the northern margin may correspond to the location of the minute grid in the then new NAD 1927 datum. For the actual corners, I think, another ellipsoid was used, probably the one above.</div><div><br></div><div>In the end, it may be necessary to just guess the true location of landmarks on the map such as road intersections or bends, or the coastline, and regeoreference using spline warping.</div><div><br></div><div>-Andreas</div><br><div class="gmail_quote"><div dir="ltr">On Fri, Nov 16, 2018 at 8:36 AM Andreas Plesch <<a href="mailto:andreasplesch@netscape.net" target="_blank">andreasplesch@netscape.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="auto"><div dir="auto">Looking at <br></div><div class="gmail_quote" dir="auto"><div dir="auto"><div dir="auto"><br></div><div dir="auto"><a href="https://ngmdb.usgs.gov/img4/ht_icons/Browse/CA/CA_Tamalpais_301790_1897_62500.jpg" rel="noreferrer noreferrer noreferrer" target="_blank">https://ngmdb.usgs.gov/img4/ht_icons/Browse/CA/CA_Tamalpais_301790_1897_62500.jpg</a></div><div dir="auto"><br></div><div dir="auto">there is a note in the lower right corner:</div><div dir="auto"><br></div><div dir="auto">Polyconic projection. To place on North American datum, move projection lines 690 ft south and 320 ft west.</div><div dir="auto"><br></div><div dir="auto"><a href="https://en.m.wikipedia.org/wiki/American_polyconic_projection" rel="noreferrer noreferrer noreferrer" target="_blank">https://en.m.wikipedia.org/wiki/American_polyconic_projection</a></div><div dir="auto"><br></div><div dir="auto">explains the projection.</div><div dir="auto"><br></div><div dir="auto">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.</div><div dir="auto"><br></div><div dir="auto">It should also be straightforward to determine if proj and therefore qgis supports the polyconic projection. It probably does.</div><div dir="auto"><br></div><div dir="auto">With that you can define a custom projection. Perhaps there is an EPSG code but I could not find it.</div><div dir="auto"><br></div><div dir="auto">EPSG 9818 seems to encode this projection although it does not seem to include the actual method in the registration.</div><div dir="auto"><br></div><div dir="auto">After you have defined a closely matching projection, you can translate the minute grid points to projected coordinates and georeference.</div><div dir="auto"><br></div><div dir="auto">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.</div><div dir="auto"><br></div><div dir="auto">Andreas</div><div dir="auto"><br></div><div dir="auto"><br><div dir="auto">From: Morgan Fletcher <<a href="mailto:morgan@hahaha.org" rel="noreferrer noreferrer noreferrer noreferrer" target="_blank">morgan@hahaha.org</a>></div><div class="gmail_quote" dir="auto"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
To: <a href="mailto:qgis-user@lists.osgeo.org" rel="noreferrer noreferrer noreferrer noreferrer" target="_blank">qgis-user@lists.osgeo.org</a><br>
Subject: [Qgis-user] Aligning georeferenced USGS historical maps<br>
Message-ID:<br>
<<a href="mailto:CAPwdt1U%2BTmE7cJR4GF63E13MPaPYWO9nsbzocHj2R8nG80duhw@mail.gmail.com" rel="noreferrer noreferrer noreferrer noreferrer" target="_blank">CAPwdt1U+TmE7cJR4GF63E13MPaPYWO9nsbzocHj2R8nG80duhw@mail.gmail.com</a>><br>
Content-Type: text/plain; charset="utf-8"<br>
<br>
I am new to GIS, an amateur who is curious about old roads. I have QGIS<br>
3.4.0 installed on OS-X 10.13.6 using the pre-built binaries available from<br>
<a href="https://download.qgis.org/" rel="noreferrer noreferrer noreferrer noreferrer noreferrer" target="_blank">https://download.qgis.org/</a>. If I visit the USGS topoView<br>
<<a href="https://ngmdb.usgs.gov/topoview/" rel="noreferrer noreferrer noreferrer noreferrer noreferrer" target="_blank">https://ngmdb.usgs.gov/topoview/</a>> page and download a historic map, for<br>
instance the geotiff archive from Tamalpais, CA 1897 (1950 ed.)<br>
<<a href="https://ngmdb.usgs.gov/topoview/viewer/#10/37.8564/-122.6336" rel="noreferrer noreferrer noreferrer noreferrer noreferrer" target="_blank">https://ngmdb.usgs.gov/topoview/viewer/#10/37.8564/-122.6336</a>>, I can add a<br>
raster layer with the .tif file from the archive and it will be placed in<br>
rough correspondence with a base map in my QGIS project. In my case my<br>
basemap is OpenStreetMap. (crs=EPSG:3857&format&type=xyz&url=<br>
<a href="http://a.tile.openstreetmap.org/%7Bz%7D/%7Bx%7D/%7By%7D.png&zmax=19&zmin=0" rel="noreferrer noreferrer noreferrer noreferrer noreferrer" target="_blank">http://a.tile.openstreetmap.org/%7Bz%7D/%7Bx%7D/%7By%7D.png&zmax=19&zmin=0</a>)<br>
The problem is that the maps don't line up, visually. For example:<br>
<br>
<br>
Screen Shot 2018-11-02 at 8.51.02 AM.png<br>
<<a href="https://drive.google.com/a/hahaha.org/file/d/0B-OybZpGWIkHUWhuWEZLS2xWZEhTUC1MMkN4X2dfZGkxQm1J/view?usp=drive_web" rel="noreferrer noreferrer noreferrer noreferrer noreferrer" target="_blank">https://drive.google.com/a/hahaha.org/file/d/0B-OybZpGWIkHUWhuWEZLS2xWZEhTUC1MMkN4X2dfZGkxQm1J/view?usp=drive_web</a>><br>
<br>
<br>
I can solve it better with georeferencer. Before I viewed Hans van der<br>
Kwast's excellent Georeferencing a scanned map and digitizing vectors in<br>
QGIS <<a href="https://youtu.be/4IWyVeGhzog" rel="noreferrer noreferrer noreferrer noreferrer noreferrer" target="_blank">https://youtu.be/4IWyVeGhzog</a>> video, I simply started finding common<br>
points; now I understand that using the correct CRS, projection and the<br>
grid is perhaps perhaps the best strategy.<br>
<br>
My questions are:<br>
<br>
<br>
- If I download a geotiff archive from topoView, is QGIS 3.4.0 correctly<br>
parsing the data in the .tif file, or the other files (.prj, .tfw) in the<br>
extracted directory, and placing the map correctly? Can it be adjusted to<br>
align better, and if so, how?<br>
- Should I use EPSG:26710 for the Tamalpais<br>
<<a href="https://ngmdb.usgs.gov/topoview/viewer/#10/37.8754/-122.6260" rel="noreferrer noreferrer noreferrer noreferrer noreferrer" target="_blank">https://ngmdb.usgs.gov/topoview/viewer/#10/37.8754/-122.6260</a>> map, and<br>
attempt to georeference it myself, using its minute grid? Why does the map<br>
border show a skew at the top left and right corners? (see below)<br>
- I have found that, to get a hand-drawn, antique map to align with a<br>
modern base map, I often have to add so many points in georeferencer that<br>
the rendered map has to be very distorted. What is the best method to get<br>
old maps to line up, so that historical roads can be related to modern<br>
roads?<br>
<br>
Skew mentioned in second point:<br>
<br>
<br>
Screen Shot 2018-11-08 at 8.20.56 AM.png<br>
<<a href="https://drive.google.com/a/hahaha.org/file/d/0B-OybZpGWIkHeEE0aDMyQVFCZ0F1R01pRGhKeEJVTzYxaEpj/view?usp=drive_web" rel="noreferrer noreferrer noreferrer noreferrer noreferrer" target="_blank">https://drive.google.com/a/hahaha.org/file/d/0B-OybZpGWIkHeEE0aDMyQVFCZ0F1R01pRGhKeEJVTzYxaEpj/view?usp=drive_web</a>><br>
<br>
<br>
I couldn't find a searchable archive of qgis-user; my apologies if these<br>
are already answered somewhere. I did ask a variation of these questions on<br>
StackExchange<br>
<<a href="https://gis.stackexchange.com/questions/301199/fix-offset-of-geotiff-file" rel="noreferrer noreferrer noreferrer noreferrer noreferrer" target="_blank">https://gis.stackexchange.com/questions/301199/fix-offset-of-geotiff-file</a>>,<br>
where it was heavily edited by 'Vince', and has no answers after a week, so<br>
asking here.<br>
<br>
Morgan<br>
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</blockquote></div></div></div>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="m_-1711798667848404960m_-6965619288249361890gmail_signature"><div dir="ltr"><div>Andreas Plesch<br>Waltham, MA 02453</div></div></div></div></div></div></div>
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