Correct autocad coordinate System for GCS_North_American_1927?

[Anonymous]

I have a geotiff map i downloaded from here http://ngmdb.usgs.gov/maps/topoview/viewer/#4/40.00/-107.51 and am wanting to put the downloaded map into a blank autocad drawing so that I can query other data into it. However I am having troulble determining what corrediante zone I am supposed to set my drawing file to. If I try to bring in the image in ESRI arcmap it says the projection is GCS_North_american_1927.  I have tried the projection of LL27 in autocad and this does not appear to be correct becuase whenever I query something into it from a differnent drawing the objects queried in are incredable small and not located correctly. 

[Pointdump]

J,

The link is kinda vague. What specific file did you download? Did it come with a World File? Sometimes there's a XML file that tells more about the coordinate system. And sometimes the website has more information about the files.

Dave

[Anonymous]

Hello,

Thanks for getting back to me. I am working with this map  http://ngmdb.usgs.gov/ht-bin/tv_download.pl?id=5294456&tif=true  and the attached file as well, the attached file should fall into part of the map I am linking to and should line up pretty decently. I can not make this happen, because I can't get the map I am linking have a correctly assigned coordinate system. Any help at all would be great!

[Pointdump]

J,

That's a cool site. Lots of interesting historical maps.

Your JPEG is not geo-referenced, so you'd have to use ALIGN to make it fit your drawing. Not difficult to do, you have Coordinates in each corner:

Better would be to get the GeoPDF or GeoTIFF. They are geo-referenced:

Dave

[Anonymous]

I have a geotiff's downloaded and am wanting to put the downloaded map into autocad, however I am having troulble determining what coordiante system I am supposed to set my drawing file to. If I try to bring in the image in ESRI arcmap it says the projection is GCS_North_american_1927.  I have tried the projection of LL27 in autocad and this does not appear to be correct becuase whenever I query in lets say that stream drawign I attached above it is not at all correct. Any idead what what  GCS_North_american_1927 translates into for autocad map?

[Pointdump]

J,

Please post your GeoTIFF(s). If they are too large for this forum, you can DropBox them.

Dave

[Anonymous]

Thanks for trying to help. https://www.dropbox.com/s/d50v0ji3tbkil71/KY_Hindman_803634_1915_62500_geo.tif.zip?dl=0

[Pointdump]

J,

Your World File (TFW) Reads thusly:

5.2916666667
0.0000000000
0.0000000000
-5.2916666667
-13120.2495785958
29522.2202616146

What it means is this:

Line 1: A: pixel size in the x-direction in map units/pixel
Line 2: 😧 rotation about y-axis
Line 3: B: rotation about x-axis
Line 4: E: pixel size in the y-direction in map units, almost always negative[3]
Line 5: C: x-coordinate of the center of the upper left pixel
Line 6: F: y-coordinate of the center of the upper left pixel

I might be overlooking something, but it doesn't look like the World File can place the TIFF in the right spot in LL27. The easiest way will be to ALIGN the TIFF to your drawing.

Dave

[Anonymous]

Thanks again, i guess that is what I will end up doing. I found this, but the guys link doesn't work. http://forums.autodesk.com/t5/autocad-map-3d-general/gcs-north-american-1927/m-p/2011647

[Anonymous]

Let me ask one last question, there is no way to get that geopdf into autocad is there? I a few years back i think the only way was through the use of dotsoft software and just wanted to see if that was still my only choice?

[Pointdump]

J,

I've never used Dotsoft, although I've heard good things about it. There's only two ways to fix your TIFF; change the insertion point or use ALIGN. Even if you change the insertion point, you still might have to play with scale. Probably easier to just use ALIGN.

Dave

[Pointdump]

J,

Here's your drawing with image correctly (I think) positioned. I used the align command. Kinda tricky, because the topo map image was in NAD27, and your drawing is NAD83.

Dave

[Pointdump · Accepted solution]

J,

Further thoughts. I used NAD27 longs and lats to position the topo map onto your NAD83 drawing. But then I thought, wait a minute, according to the XML file the map was originally published in 1915 (says 1915 pubdate). So the map was created before the NAD27 datum came into existence.

In the XML file, it says this:
"Scanned TIFF images are georeferenced to the original map datum, and reprojected to the original map projection." The original map projection is listed as "Polyconic". Then it shows their scan projected as Meters, NAD27 datum, Clarke 1866 Ellipsoid.

So what I did was this: I opened a drawing in KY South NAD27. I MAPIINSERT'ed the scanned image, then used the four called-out locations of the map corners to ALIGN and scale the map. Close that drawing. Open up the drawing in KY Single Zone, Attach the NAD27 drawing, Query the map, Unattach, Save drawing. So you'll notice the corners of the map aren't the same longs and lats in NAD83 as they are in NAD27.

Dave

[Anonymous]

Thanks for all your time on this, i wish autodesk would add in that GCS_North_American_1927 into their list of coordinate systems. It seems that all your efforts resulted in pretty much an identical match of how this looks in arcmap, something that has the GCS_North_American_1927 system. Thank you again, I now have a pattern down on how to do this and I guess anybody else does as well that runs across this post in the future :).