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 <[email protected]> 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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