Trying this again. Thanks, Mike Flanagan, for trying to help me the first
time.
I start a new project in QGIS 3.12. I have a USGS
map CA_Concord_297163_1915_62500_geo.tif, downloaded from here
<https://ngmdb.usgs.gov/topoview/viewer/#11/37.8612/-122.0759>, the
"Concord, CA 1915, 1915 edition" map. I add "Google Maps" from Browser >
XYZ Tiles as a base map. My project properties show WGS/84 Pseudo-Mercator,
EPSG:3857. I select Layer > Add Layer > Add Raster Layer... > I can select
this geotiff. Clicking Add brings up this dialog. What do I choose?
Screen Shot 2020-04-18 at 12.54.31 PM.png
<https://drive.google.com/file/d/1FKVPrHLtXXKK8a-QTTz3IigT9dpj1Hou/view?usp=drive_web>
What do I choose?
The reason why I ask, is that all my usgs maps are offset from the base map
enough to be maddening. I know these things are imperfect, but even the
corners labeled with known points are off. Below is the gdalinfo output for
this file. Last question; if I georeference this tif file, versus trusting
its metadata, the top corners left and right have two divergent borders.
They start from a common point at bottom and at the top they are maybe a
degree apart. Which of these two endpoints matches the stated coordinate?
Morgans-MBP-2:CA_Concord_297163_1915_62500_geo_tif morganfletcher$
/Applications/QGIS3.12.app/Contents/MacOS/bin/gdalinfo
CA_Concord_297163_1915_62500_geo.tif
Driver: GTiff/GeoTIFF
Files: CA_Concord_297163_1915_62500_geo.tif
Size is 4775, 5908
Coordinate System is:
PROJCS["unnamed",
GEOGCS["NAD27",
DATUM["North_American_Datum_1927",
SPHEROID["Clarke 1866",6378206.4,294.9786982138982,
AUTHORITY["EPSG","7008"]],
AUTHORITY["EPSG","6267"]],
PRIMEM["Greenwich",0],
UNIT["degree",0.0174532925199433],
AUTHORITY["EPSG","4267"]],
PROJECTION["Polyconic"],
PARAMETER["latitude_of_origin",0],
PARAMETER["central_meridian",-122.125],
PARAMETER["false_easting",0],
PARAMETER["false_northing",0],
UNIT["metre",1,
AUTHORITY["EPSG","9001"]]]
Origin = (-12632.067326823029362,4208868.700336153618991)
Pixel Size = (5.291666666666666,-5.291666666666640)
Metadata:
AREA_OR_POINT=Area
TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch)
TIFFTAG_XRESOLUTION=300
TIFFTAG_YRESOLUTION=300
Image Structure Metadata:
COMPRESSION=YCbCr JPEG
INTERLEAVE=PIXEL
SOURCE_COLOR_SPACE=YCbCr
Corner Coordinates:
Upper Left ( -12632.067, 4208868.700) (122d16' 7.84"W, 38d 0'50.81"N)
Lower Left ( -12632.067, 4177605.534) (122d16' 5.87"W, 37d43'56.80"N)
Upper Right ( 12635.641, 4208868.700) (121d58'52.01"W, 38d 0'50.81"N)
Lower Right ( 12635.641, 4177605.534) (121d58'53.98"W, 37d43'56.80"N)
Center ( 1.787, 4193237.117) (122d 7'29.93"W, 37d52'24.13"N)
Band 1 Block=512x512 Type=Byte, ColorInterp=Red
Overviews: 2388x2954, 1194x1477, 597x739, 299x370, 150x185, 75x93, 38x47
Band 2 Block=512x512 Type=Byte, ColorInterp=Green
Overviews: 2388x2954, 1194x1477, 597x739, 299x370, 150x185, 75x93, 38x47
Band 3 Block=512x512 Type=Byte, ColorInterp=Blue
Overviews: 2388x2954, 1194x1477, 597x739, 299x370, 150x185, 75x93, 38x47
On Sat, Apr 18, 2020 at 2:43 PM Morgan Fletcher <morgan at hahaha.org> wrote:
> (Resending, with screenshots as google drive links, to cut down message
> size.)
>
> I am running 3.12.1-București on a mac, os-x 10.14.6. My knowledge of GIS
> is rudimentary, I've learned what I need to, to satisfy my curiosity about
> my region, using old maps.
>
> I have downloaded all the USGS maps for my region - Oakland, CA, USA,
> which corresponds to "CA Concord" - from USGS topoView, in geotiff format.
> Opening them in QGIS gives fairly wild offsets; they are not all encoded
> the same way, yet have common corners. Features on the map vary with what
> modern maps show, but getting their corners right would help me a lot.
>
> If I create a new project, set my CRS to WGS 84 / Pseudo-Mercator
> (EPSG:3857) as I think is correct for my base map, Google Maps (EPSG:3857 -
> WGS 84 / Pseudo-Mercator - Projected) then Layer > Add Layer > Add Raster
> Layer > Raster Dataset > CA_Concord_465520_1943_62500_geo.tif > Add, I get
> prompted with:
>
>
> https://drive.google.com/file/d/1FKVPrHLtXXKK8a-QTTz3IigT9dpj1Hou/view?usp=sharing
>
> I don't know what to choose, here. I chose the first one. I've tried
> others. The tif.prj file does say
> DATUM["D_North_American_1927",SPHEROID["Clarke_1866",6378206.4,294.9786982]],
> which I am guessing conforms to NAD27. If I add an opacity slider to the
> new raster layer, set its opacity, and then use the Zoom to Coordinate
> panel to navigate to 37º45'N 122º15'W, I find that the point is off from
> what's on the map, see:
>
>
> https://drive.google.com/file/d/10vYtcM1FZ-vdS3z1FPW2EYbrNy2sj65L/view?usp=sharing
>
> This is similarly true at the top left:
>
>
> https://drive.google.com/file/d/18naBKuwk6rZ9DP0tFOZxnGKlIpRQgDKM/view?usp=sharing
>
> Also, note how the map shows two lines at top left, it's true at top
> right. This is something to do with projection, I think. I've tried to
> georeference these lines, to get them to line up right, but which
> intersection do I use, when there are two vertical lines intersecting with
> the top, horizontal border, to reference 122º 15' 38º 00' ? I've had
> mixed results, trying to use deg-min-ss coordinates to georeference these;
> I get a map off the west coast of Africa. Using points on the map is more
> successful.
>
> All the maps have slightly variant values in their tfw files. Their prj
> files are more uniform, but also show variations. I'd like to normalize
> them all, so that I can view the USGS topo maps for my region over time.
> Advice?
>
> Thanks,
>
> Morgan
>
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