Oahu maps off center

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Oahu maps off center

Postby hikenewhampshire » Thu Feb 24, 2011 10:36 am

The USGS quads for Oahu are offset E-W from the usual grid to cover the island with fewer quads, for instance Schofield Barracks runs from 158-01-30 to 158-09

LoJ however uses the traditional grid thus locating many summits on the wrong map

Look at the entry for Pu‘ulanipō, for example:
From GNIS http://geonames.usgs.gov/pls/gnispublic ... FID:363909
Pu‘ulanipō 363909 Summit Honolulu HI 212006N 1574545W 1194 Koko Head 01-JAN-2000 30-SEP-2003

From LoJ http://listsofjohn.com/PeakStats/Climbers.php?Id=107823
Pu'ulanipō
Elevation : 2,621'
HI Peaks Rank : 81
Counties : Honolulu
Quad : Honolulu
Coords : 21.3318°N, 157.7597°W
Rise : 601'
Saddle : 2,020'
Line Parent : 3150
Proximate Parent : 3150
Isolation : 2.58 miles
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Re: Oahu maps off center

Postby John Kirk » Thu Feb 24, 2011 2:12 pm

There are a lot of reasons that this was done intentionally.
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a warning would be nice

Postby hikenewhampshire » Thu Feb 24, 2011 4:09 pm

I can see how if the database is set up to work off a grid it might be hard to accommodate map names off grid.

But how about storing the map name as A/B where those are the 2 maps that might be correct for that grid?
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Re: Oahu maps off center

Postby John Kirk » Thu Feb 24, 2011 9:46 pm

The problem is that the offsets are not uniform among the islands and differ even on the same island such that a match cannot be performed on coordinate offsets for adjacent quadrangles (like offsetting the NE coordinate minus or plus .125 degrees):
Molokai
Kauai
Lanai
Hawaii
Oahu
Notice that widths and heights vary on the same grid.

In my view, in this era of seamless electronic maps, I have fixed the USGS's self-contradiction by enforcing 7.5 minute interval bounding coordinates.

To set up something to accommodate the ridiculous USGS bounding coordinates with all the current quad-based functionality would probably take 30-40 developer hours that I currently don't have, involving a separate quad table schema, new lookup rules, case handling.

I can put in some notes appear on the peak profile pages when Hawaii is in scope...
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Re: Oahu maps off center

Postby hikenewhampshire » Sat Feb 26, 2011 12:13 pm

Right now, the quad name appearing in "Peak Stats" may not be the correct name, and if you ask for all peaks in a quad you probably won't get a correct list

What I am suggesting is that you retain your grid but name each square by all the quad names partially in that square, that eliminates the above problems

The grid offset issue is not unique to Hawaii and may bite you in other states, a more comprehensive solution would be to store the coordinate corners for each grid square but I can see how that is more work
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Re: Oahu maps off center

Postby John Kirk » Sun Feb 27, 2011 12:12 pm

What I am suggesting is that you retain your grid but name each square by all the quad names partially in that square

Up to nine quad names as a quad name is not a good solution (offsets are not just e-w)

The grid offset issue is not unique to Hawaii and may bite you in other states

Other states... such as?
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Re: Oahu maps off center

Postby hikenewhampshire » Sun Mar 06, 2011 5:25 pm

John Kirk wrote:
The grid offset issue is not unique to Hawaii and may bite you in other states

Other states... such as?

Well, the first three states I checked all have this issue on some quads:
North Islands, LA
South Manitou Island, WI
Whitefish Point, MI

I know it's true elsewhere but I think that's enough to show that it does happen.
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