[Qgis-user] Dumb USGS geotiff questions

Tue May 5 23:10:44 PDT 2020

Hi Morgan,

i would suggest to NOT use Pseudo Mercator as the projects CRS and therefore
also not the Google Maps Layer as a Base Layer. Pseudo Mercator is from my
experience simply not made for these kinds of work, because its accuracy is
limited especially when it comes to locations away from the equator.

As your work requires a decent accurate reference layer i would suggest you
seek out a reference layer in a appropriate projection like UTM or LAEA
depending on the extent of your study area. Your local authorities may
provide you with this data, for example.

Regarding your specific question QGIS will from time to time ask you for the
transformation to use when in doubt. I mostly check the first option because
i cannot be bothered to look further than the estimated accuracy.

Cheers
Jonas

Morgan Fletcher wrote
> 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@

> > 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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