Mtn_Bkng_Dave
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Posts posted by Mtn_Bkng_Dave
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http://www.ngs.noaa.gov/datasheet.html#NGSmap
This link will allow you to look up the complete NGS datasheet. It will have all of the datum history including coords for each control point that were established with each survey datum.
WGS84 typically is not included on the NGS. I guess the ellipsoidal shape of the earth has not changed much since 1983 so the datasheets haven't had a new datum established.
WGS84 was introduced as a "New World Order" so to speak to globally calibrate datums so that GPS systems would work properly no matter where you are. I guess since the US owns most of the GPS technology in public, private and military sectors they started with NAD83 as the base and converted the rest of the world to that datum to produce WGS84.
But enough rambling.... the page link has all the datums for each point. Go check it out and play with your gps. Switch datums on your GPS and plug in all the numbers and see which ones work the best. Could add an interesting twist to the game.
Mtn_Bkng_Dave
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Check the coords here.
http://www.ngs.noaa.gov/datasheet.html#NGSmap
This is the link to the NGS database.
You can search by PID or Location.
Neat but slow.
But we have to live with it!
Mtn_Bkng_Dave
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Check the coords here.
http://www.ngs.noaa.gov/datasheet.html#NGSmap
This is the link to the NGS database.
You can search by PID or Location.
Neat but slow.
But we have to live with it!
Mtn_Bkng_Dave
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Its according to the type of control point you are looking at. You are correct that some are only vertical control points. However some are horizontal control points and some are horizontal and vertical. At least they are here on the east coast. At least I hope so or we moved all that dirt from the wrong place for this shopping center!
Mtn_Bkng_Dave
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Its according to the type of control point you are looking at. You are correct that some are only vertical control points. However some are horizontal control points and some are horizontal and vertical. At least they are here on the east coast. At least I hope so or we moved all that dirt from the wrong place for this shopping center!
Mtn_Bkng_Dave
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A datum describes the model that was used to match the location of features on the ground to coordinates and locations on the map. Maps all start with some form of survey. Early maps and surveys were carried out by teams of surveyors on the ground using transited and distance measuring "chains". Surveyors start with a handful of locations in "known" positions and use them to locate other features. These methods did not span continents well. Frequently they also did not cross political borders either. The "known points" and their positions are the information that the map datum is based. As space based surveying came into use, a standardized datum based on the center of the earth was developed.
Every map that shows a geographic coordinate system such as UTM or Latitude and Longitude with any precision will also list the datum used on the map.
The Global Positioning System uses an earth centered datum called the World Geodetic System 1984 or WGS 84. WGS 84 was adopted as a world standard from a datum called the North American Datum of 1983 or NAD 83. For all practical purposes there is no difference between WGS 84 and NAD 83.
Most USGS topographic maps are based on an earlier datum called the North American Datum of 1927 or NAD 27. (Some GPS units subdivide this datum into several datums spread over the continent. In the Continental United States use NAD27 CONUS.)
In the Continental United States the difference between WGS 84 and NAD 27 can be as much as 200 meters.
You should always set your GPS unit's datum to match the datum of the map you are using.
On a USGS topographic map the datum information is in the fine print at the bottom left of the map. The datum will always be NAD 27. There may be information on how many meters to shift a position to convert it to NAD 83. Think of this as the error that will be introduced if you leave your GPS unit set to WGS 84. A dashed cross in the SW and NE corners of the map gives a visual indication of the difference between the two datums.
FYI,
Mtn_Bkng_Dave
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A datum describes the model that was used to match the location of features on the ground to coordinates and locations on the map. Maps all start with some form of survey. Early maps and surveys were carried out by teams of surveyors on the ground using transited and distance measuring "chains". Surveyors start with a handful of locations in "known" positions and use them to locate other features. These methods did not span continents well. Frequently they also did not cross political borders either. The "known points" and their positions are the information that the map datum is based. As space based surveying came into use, a standardized datum based on the center of the earth was developed.
Every map that shows a geographic coordinate system such as UTM or Latitude and Longitude with any precision will also list the datum used on the map.
The Global Positioning System uses an earth centered datum called the World Geodetic System 1984 or WGS 84. WGS 84 was adopted as a world standard from a datum called the North American Datum of 1983 or NAD 83. For all practical purposes there is no difference between WGS 84 and NAD 83.
Most USGS topographic maps are based on an earlier datum called the North American Datum of 1927 or NAD 27. (Some GPS units subdivide this datum into several datums spread over the continent. In the Continental United States use NAD27 CONUS.)
In the Continental United States the difference between WGS 84 and NAD 27 can be as much as 200 meters.
You should always set your GPS unit's datum to match the datum of the map you are using.
On a USGS topographic map the datum information is in the fine print at the bottom left of the map. The datum will always be NAD 27. There may be information on how many meters to shift a position to convert it to NAD 83. Think of this as the error that will be introduced if you leave your GPS unit set to WGS 84. A dashed cross in the SW and NE corners of the map gives a visual indication of the difference between the two datums.
FYI,
Mtn_Bkng_Dave
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Any chance on including the Order (accuracy) of the benchmarks? Your search engine works so much better than the USGS NOAA site it would make bringing in first order points with my Trimble so much easier!
Mtn_Bkng_Dave
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Any chance on including the Order (accuracy) of the benchmarks? Your search engine works so much better than the USGS NOAA site it would make bringing in first order points with my Trimble so much easier!
Mtn_Bkng_Dave
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quote:
Originally posted by paul_stratton:I've created a spreadsheet and procedure on explaining how to create the shortest route to the nearest 25 Geocache waypoints. I use the waypoints downloaded using EasyGPS then use the GPS and a spreadsheet to do the computations.
Enjoy! The files, in a compressed zipped file, are located in the "Friends" folder at
http://briefcase.yahoo.com/bc/strattonpaul
let me know what you think!
paul_stratton@sbcglobal.net
I think the Datum is wrong.
in Benchmarking
Posted
http://www.ngs.noaa.gov/datasheet.html#NGSmap
This link will allow you to look up the complete NGS datasheet. It will have all of the datum history including coords for each control point that were established with each survey datum.
WGS84 typically is not included on the NGS. I guess the ellipsoidal shape of the earth has not changed much since 1983 so the datasheets haven't had a new datum established.
WGS84 was introduced as a "New World Order" so to speak to globally calibrate datums so that GPS systems would work properly no matter where you are. I guess since the US owns most of the GPS technology in public, private and military sectors they started with NAD83 as the base and converted the rest of the world to that datum to produce WGS84.
But enough rambling.... the page link has all the datums for each point. Go check it out and play with your gps. Switch datums on your GPS and plug in all the numbers and see which ones work the best. Could add an interesting twist to the game.
Mtn_Bkng_Dave