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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Dean,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Perfectly said! Thank you for your
insight. What is interesting is we are doing an evaluation of Discovery
on OpenWorks and the original recommendation that Halliburton was to store all
data in some projected coordinate system as OpenWorks is so Landmark seismic oriented.
But were are looking for a robust corporate well data store and have operations
from the Rockies to the Gulf and New Mexico to Appalachia, so a single
projected system is not practical. The new version of OpenWorks at least
stores both the original coordinates and the master projected be it x, y or
lat/lon.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>David<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<hr size=2 width="100%" align=center tabindex=-1>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> Dean C.
Mikkelsen [mailto:dcmikkelsen@shaw.ca] <br>
<b><span style='font-weight:bold'>Sent:</span></b> Sunday, October 07, 2007
3:48 PM<br>
<b><span style='font-weight:bold'>To:</span></b> 'David M. Baker';
gdal-dev@lists.maptools.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> RE: [Gdal-dev] A Question
of Coordinate Storage</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<div>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>Hi David,</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>There is often a misunderstanding between
accuracy and precision, but essentially all things come down to the quality of
data and the accuracy required for intended purpose.</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>Having worked in the oil industry for many
years (w/Schlumberger) where I encountered this same problem with the Gulf of
Mexico datasets, and more and more data being acquired in WGS84, yet the MMS
required at the time, the data to be reported in NAD27 (in fact many oil
companies still kept the data in NAD27 due to the apparent cost of coverting
data between the two - BP is now just undertaking this exact process due to a
change in gov't legislation and a lobby group here in Canada (CAPP)
finally recommending that the data be stored in WGS84), and it is interesting
to note, as we go to deep water offshore GOM, there is hardly any NAD27 control
(in fact only three points measured on wells), which makes the transformation
between NAD27 and NAD83 very questionable (less control, less parameters for
the transformation between the two systems), so the surveyors used their own
control networks.</span></font><o:p></o:p></p>
</div>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>The recommendation that we adopted (as was
applied to products such as GeoFrame, Finder, OpenWorks) was to store
coordinates in lat/long in WGS84 and let the software handle the map projection
transformation as the speed was hardly noticeable - this became the
default for the software. It was felt best to store the data in a defined ECEF
coordinate system. There is no need to compound the error, but instead maintain
the errors at a level that you know and understand. By moving the data to
WGS84, you will know the level of error and be able to assign some level of
quality to the data. I would still avoid storing everything in a map
projection, specifically for a specific zone, as you have a large area.</span></font><o:p></o:p></p>
</div>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>Historical data provides obstacles, but
there is often other points to consider as well with the data quality and even
the monumentation (metes and bounds, etc.) done at the time and what is
available currently (presently).</span></font><o:p></o:p></p>
</div>
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<div>
<p><font size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:blue'>Cheers,</span></font><font color=blue><span style='color:
blue'><o:p></o:p></span></font></p>
<p><font size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:blue'>Dean</span></font><font color=blue><span style='color:blue'><o:p></o:p></span></font></p>
<p><font size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:blue'>Dean C. Mikkelsen, B.Sc., P.Eng.</span></font><font
color=blue><span style='color:blue'><o:p></o:p></span></font></p>
<p><font size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:blue'>Terra ETL Ltd. - <a href="http://www.terraetl.com">http://www.terraetl.com</a></span></font><font
color=blue><span style='color:blue'><o:p></o:p></span></font></p>
<p><font size=3 color=blue face="Times New Roman"><span style='font-size:12.0pt;
color:blue'> <o:p></o:p></span></font></p>
</div>
<blockquote style='margin-top:5.0pt;margin-right:0in;margin-bottom:5.0pt'>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=2 face=Tahoma><span
style='font-size:10.0pt;font-family:Tahoma'>-----Original Message-----<br>
<b><span style='font-weight:bold'>From:</span></b> David M. Baker
[mailto:dmbaker@cox.net] <br>
<b><span style='font-weight:bold'>Sent:</span></b> Sunday, October 07, 2007
12:47 PM<br>
<b><span style='font-weight:bold'>To:</span></b> dcmikkelsen@shaw.ca;
gdal-dev@lists.maptools.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> RE: [Gdal-dev] A Question
of Coordinate Storage</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Dean,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Thanks for the link you provided.
There is a lot on info on this subject germane to my problem. Please see
a reply I made to Frank earlier. We are not proposing storing our
corporate data in NAD27 even though most of us geoscientists do in our local
database (because most of our vendor data come in NAD27). I guess I need
to do some testing similar to those referred to here: <a
href="http://srmwww.gov.bc.ca/gis/bceprojection.html">http://srmwww.gov.bc.ca/gis/bceprojection.html</a>.
The GIS guys claim greater accuracy, though I think they mean precision, but
the fact is our data is not that accurate. If we are within a meter we
are doing well, though if I new for sure we were within 5 meters I would be
happy. We have old data that is measured off a Jeffersonian gird system
and converted to NAD27 lat/lons, we have newer, survey, data that referenced to
state plain and then converted to NAD27 lat/lon, but more recently we get data
that the positions are acquired by GPS and reported in WGS84. So we start
with a real provenance problem, but we live with that. What concerns me
is potential for compounding or needlessly adding error for the sake of speed
in our map display.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>David<o:p></o:p></span></font></p>
<div>
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face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center tabIndex=-1>
</span></font></div>
<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> Dean C.
Mikkelsen [mailto:dcmikkelsen@shaw.ca] <br>
<b><span style='font-weight:bold'>Sent:</span></b> Sunday, October 07, 2007
11:55 AM<br>
<b><span style='font-weight:bold'>To:</span></b> 'David M. Baker';
gdal-dev@lists.maptools.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> RE: [Gdal-dev] A Question
of Coordinate Storage</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<div>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>Hi David,</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>I would recommend keeping all the
co-ordinates in geographics (latitude/longitude), rather than UTM Zone 14.
Keeping all the data in one zone for an area that covers 3 to 5 UTM Zones does
not make sense from a mapping point of view or even from a data conversion
point of view.</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>Essentially your error is increasing
exponentially the further away you go from the <st1:place w:st="on">Central Meridian</st1:place>
in the UTM Projection. The more zones you cover, the greater the error in the
values. Not only that, as you transform the coordinates back and forth from UTM
14 to geographic to UTM 12, 18, 15, etc., you will also be introducing
errors again. Then if you reproject to a different datum, say NAD83, you are
introducing another error (even if you are using a grid conversion, such as
NADCON (larger error if you are using a Molodensky conversion).</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>For example, here in <st1:place w:st="on"><st1:State
w:st="on">British Columbia</st1:State></st1:place>, even using ArcSDE,
coordinates are stored in geographics (and we are covering 5 UTM Zones,
but have settled upon an Albers Projection - for mapping, and NAD83 for the
datum). For working in ArcSDE, take a look here: <a
href="http://srmwww.gov.bc.ca/gis/sdedata.html">http://srmwww.gov.bc.ca/gis/sdedata.html</a>.
Note that even the BC Gov't states that for working outside B.C., that
there "needs a different spatial reference, even if it is stored in
geographic or BC Albers projection. Data in this larger area must have a lower
resolution".</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>Remember, coordinates that are stored
in latitude and longitude are usually stored as two real numbers in
decimal degrees and we know that these range from -180.0 W to +180.0 E in
longitude, and -90.0 S to +90.0 N in latitude, for a total of 360.0 degrees
around the earth in each direction. The earth's circumference is roughly 40,000
kilometres or 40,000,000 metres and therefore one can conclude there are
about </span></font><o:p></o:p></p>
<pre><font size=2 color=blue face=Arial><span style='font-size:10.0pt;
font-family:Arial;color:blue'> <o:p></o:p></span></font></pre><pre><font
size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:blue'> 40,000,000 <o:p></o:p></span></font></pre><pre><font size=2
color=blue face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:blue'> ---------- <o:p></o:p></span></font></pre><pre><font
size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:blue'> 360</span></font><o:p></o:p></pre><pre><font
size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:blue'><o:p> </o:p></span></font></pre><pre><font size=2 color=blue
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:blue'>or about 111,000 metres per degree of latitude anywhere on the earth. The size of a degree of longitude varies - at the equator it's the same as a degree of latitude, but at the poles it is 0. </span></font><o:p></o:p></pre>
<p><font size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:blue'>9 significant digits is sufficient to preserve metre
precision (this would be number (9,6) in Oracle), or 11 significant digits to
preserve centimetre precision (this would be number (11,8) in Oracle).</span></font><o:p></o:p></p>
<p><font size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:blue'>Also note that by restricting the range (extent) of the area
that can be included in a dataset, it is possible to increase the precision of
the coordinates stored - therefore I would not store everything in UTM
14. I would only keep the coordinates in UTM 14 if that was my only are of
interest, otherwise keep it geographic (latitude and longitude). UTM is LESS
PRECISE after all the conversions and especially since we are talking about 3
to 5 zones.</span></font><o:p></o:p></p>
<p><font size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:blue'>I would also recommend that your GIS department move their
data into NAD83/WGS84, not NAD27. WGS84 is a precisely determined system, while
NAD27 is not. NAD27 is based on triangulations being joined together to form a
model of the earth, which is centered at Meades Ranch, <st1:place w:st="on"><st1:State
w:st="on">Kansas</st1:State></st1:place>, while WGS84 is ECEF (Earth Centered
Earth Fixed) and determined by Satellite Measurements. NADCON is an accurate
conversion for most mapping and GIS use, so you should be safe there. I would
also look at your local HARN network or any local geodetic work done by your
State Gov't Agency to see what they recommend.</span></font><o:p></o:p></p>
<p><font size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:blue'>Let me know if I can expand further or answer more questions.</span></font><o:p></o:p></p>
<p><font size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:blue'>Cheers,</span></font><o:p></o:p></p>
<p><font size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:blue'>Dean</span></font><o:p></o:p></p>
<p><font size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:blue'>Dean C. Mikkelsen, B.Sc., P.Eng.</span></font><o:p></o:p></p>
<p><font size=2 color=blue face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:blue'>Terra ETL Ltd. - <a href="http://www.terraetl.com">http://www.terraetl.com</a></span></font><o:p></o:p></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> <o:p></o:p></span></font></p>
</div>
<blockquote style='margin-top:5.0pt;margin-right:0in;margin-bottom:5.0pt'>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=2 face=Tahoma><span
style='font-size:10.0pt;font-family:Tahoma'>-----Original Message-----<br>
<b><span style='font-weight:bold'>From:</span></b>
gdal-dev-bounces@lists.maptools.org [mailto:gdal-dev-bounces@lists.maptools.org]
<b><span style='font-weight:bold'>On Behalf Of </span></b>David M. Baker<br>
<b><span style='font-weight:bold'>Sent:</span></b> Sunday, October 07, 2007
8:40 AM<br>
<b><span style='font-weight:bold'>To:</span></b> gdal-dev@lists.maptools.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> [Gdal-dev] A Question of
Coordinate Storage</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>All,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Though this question is not specific to GDAL, OGR or
FWTools, I believe some of the most knowledgeable people of the subject are on
this mailing list and hope you will allow me to ask.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>At my company, there is an ongoing debate as to the best
coordinate system to store cooperate spatial data in. The debate is
mainly between the Geoscience department and the GIS department. The vast
majority of the data the Geo’s use comes from public sources that are in
geographic lat/lon in NAD27. This data is then reprojected for mapping
and display in various coordinate systems, state plane and UTM (zones 12
– 18, but mostly in 13, 14 and 15). The GIS guys supply many layers
to the Geo’s for display. They are currently upgrading from ArcSDE
9.1 to 9.2, and in the process are converting all their coordinates for storage
in UTM zone 14. GIS made the comment that this is a much more accurate
way to store the data, that geographic coordinates are less precise, though,
their main reason for storing the data in a projected system is to avoid having
to do any coordinate conversion on the fly when displaying the data on
corporate web maps. The layers supplied to the Geo’s will need to
be reprojected if their current map projections are not UTM Zone 14.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>The question: is it wise to store coordinates that cover
such a wide area in a single projected coordinate system, or would it be better
to store them in some geographic coordinate system, e.g., NAD83 or WGS84?
And if this not the best way (UTM14), why? What are the pitfalls?
Is it really more accurate, or precise to store data in a Cartesian coordinates
and suffer the conversion to a different projection as needed?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Thanks,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>David<o:p></o:p></span></font></p>
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