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#1
Kevin McManigal

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My next challenge is for the projection masters, should they choose to accept it.

I have a map that was traced off of a USGS 250,000 topographic paper map. The original states that it was last updated in 1974, but the datum information in the left corner says it was compiled from a range of aerial photos and different scale maps. I assume that it is in NAD 27, but it also says that the grid is based on the Colorado coordinate system. It is projected in the Transverse Mercator.

A DRG of the same map downloaded from the USGS is in NAD 83/UTM zone 13. I assume that it has been transformed with NADCON.

Here is the rub: The map that I just geo-reference will not line up with the digital map it was traced from. I exported the shape files from FH, then assigned a NAD 27/ UTM zone 13 to them in ArcCatalogue . When I open them in ArcMap over the DRG, they are converted with NADCON to NAD 83, but the roads are a about a ΒΌ mile off. I also tried to assign NAD 83 from the start, but the result is the same. So, I tried State Plane in the North Colorado zone. Same thing!

Any thoughts, ideas, or suggestions?

Thanks, Kevin
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#2
Kevin McManigal

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Crickets..... chirp,chirp. Bueller?, Bueller? Anyone!!

:P
Kevin McManigal
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#3
Casey Greene

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I know this is not really an answer, but I would call USGS and ask them what the deal is with that NAD27 map. If they really did just piece-it-together from various maps and aerial photos, you might not ever get a precise NAD83 fit.

The only other thing I can think of is messing with the units of measurement (feet/meters).

Also, here is some info on the Colorado Coordinate System that might be of use.

Good Luck :)
Casey Greene - Cartographer - Adventure Cycling Association
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#4
jblairpdx

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I'm no Projection Master, but I did survive a NAD27 -> NAD83 conversion. The first thing that comes up when I see a 27/83 mismatch is HARN:

http://www.ngs.noaa.....shtml#WhatHARN

Hearing or reading anything about HARN is enough to put anyone to sleep, unless they're tearing their hair out about why things aren't lining up. The shift seems to indicate it is more likely a coordinate problem; I remember in the Eugene (OR) area, we were getting about 300-ft shifts between NAD83 and NAD83HARN.

If the USGS data is in fact HARN-ed, it's just one more coordinate system conversion step. The likely needed projection conversion file in ArcGIS is:

NAD 1983 HARN StatePlane Colorado North FIPS 0501 Feet.prj

Then again, I'm entirely guessing.

#5
Kevin McManigal

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Ah, the plot thickens!

Turns out that the Colorado Coordinate System is in Lambert Conformal Conic. But I assume the USGS must have standardized the whole paper map into UTM. (You what happens when you assume!)

And now there is a possibility that HARN has also muddied the NAD conversions. Adding HARN into the conversion didn't seem to change a thing. So, I know more, but am even more confused!

Thanks for the suggestions.
Keep them coming.

Kevin
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#6
Kalai Selvan

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I faced the same problem, i was working on 1:250000 scale geological map, every aspect of the map finalization was over, when i changed the project to UTM NAD 27 Zone 12 USA. It was lining up away from the actual backdrop scan.

Luckily my 100 hrs of work was saved, when my client took the responsibility to look into this, coz the data was provided by him, after that i was not updated what went...Positive side, the data that i produced was useful to the client, with some rectification in the projection.

But in your case, its going to be a cricket game, where we are not sure when the ball will come ur path.

Good luck kevin.

gisguru

Thanks and Regards
Kalai Selvan





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