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301

Accuracy is the tendency of your measurements to agree with the true values. Precision is the degree to which your measurements pin down an actual value. The question is about an interplay of accuracy and precision. As a general principle, you don't need much more precision in recording your measurements than there is accuracy built into them. Using too ...


95

The Wikipedia page Decimal Degrees has a table on Degree Precision vs. Length. Also the accuracy of your coordinates depends on the instrument used to collect the coordinates - A-GPS used in cell phones, DGPS etc. decimal places degrees distance ------- ------- -------- 0 1 111  km 1 0.1 11.1 km ...


26

Here's my rule of thumb table... Latitude coordinate precision by the actual cartographic scale they purport: Decimal Places Aprox. Distance Say What? 1 10 kilometers 6.2 miles 2 1 kilometer 0.62 miles 3 100 meters About 328 feet 4 10 meters About 33 feet 5 ...


21

This question assumes an ellipsoidal model of the earth. Its reference surface is obtained by rotating an ellipse around its minor axis (plotted vertically by convention). Such an ellipse is just a circle that has been stretched horizontally by a factor of a and vertically by a factor of b. Using the standard parameterization of the unit circle, t --> ...


13

Manually reversing the rotation should do the trick; there should be a formula for rotating spherical coordinate systems somewhere, but since I can't find it, here's the derivation ( ' marks the rotated coordinate system; normal geographic coordinates use plain symbols): First convert the data in the second dataset from spherical (lon', lat') to (x',y',z') ...


12

The principal radius of the WGS84 spheroid is a = 6378137 meters and its inverse flattening is f = 298.257223563, whence the squared eccentricity is e2 = (2 - 1/f)/f = 0.0066943799901413165. The meridional radius of curvature at latitude phi is M = a(1 - e2) / (1 - e2 sin(phi)^2)^(3/2) and the radius of curvature along the parallel is N = a / (1 - e2 ...


12

It depends on what you mean by 'Universal Coordinate System'. If you wonder whether most Professionals understand Latitude and longitude, well in that case it is pretty much universally understood. But if you ask, whether it is used by everyone, then the answer is a resounding, No. There are many reasons why people use projected coordinate systems instead ...


11

I'll try to explain it in different terms: Earth's equatorial circumference is about 40,000 kilometers (25,000 miles). A latitude/longitude value breaks that distance up into 360 degrees, starting at -180 and ending at 180. This means that one degree is 40,000 km (or 25,000 miles) divided by 360: 40,000 / 360 = 111 25,000 / 360 = 69 (So, one degree ...


10

I've answered this question in passing while answering another of your question. The Greenwich Observatory was defined as a prime meridian, based on the observations by the astronomer Sir George Airy in 1851. London was selected as the official prime meridian for international maps by the International Meridian Conference in 1884. When you use a GPS, by ...


9

Try this formula (assuming your source is WGS1984, if not then you'll need to adjust the ellipsoid used by the second line): area = rad(x2 - x1) * (2 + sin(rad(y1)) + sin(rad(y2))) + rad(x3 - x2) * (2 + sin(rad(y2)) + sin(rad(y3))) + rad(x4 - x3) * (2 + sin(rad(y3)) + sin(rad(y4))) + rad(x5 - x4) * (2 + sin(rad(y4)) + sin(rad(y5))) area = abs(area * ...


9

Looks like ogr2ogr has support for exactly this problem. The below is copied directly from that page: How do I flip coordinates when they are not in the expected order The EPSG has a recommanded order for geographic SRS where the coordinates tuples of a geometry must appear in the (latitude, longitude) order, whereas most GIS will properly display such ...


9

Seems to be http://en.wikipedia.org/wiki/UN/LOCODE Coordinate syntax explained in http://www.unece.org/fileadmin/DAM/cefact/locode/Service/LocodeColumn.htm#Coordinates 1.10 Column "Coordinates" This column contains the geographical coordinates (latitude/longitude) of the location, if there is any. In order to avoid unnecessary use of ...


9

A lat lays flat. Can't think of a matching one for longitude.


9

I always remember Longtitude as being "Long", where the lines do not change in length, and circle the globe. Also, Latitude being lateral, i.e. sideways


7

For an automated ArcGIS solution, try the following in model builder: Add a new field "Latitude". Calculate the "Latitude" field using Calculate Field: !SHAPE.FirstPoint.Y! (see attached field calculator screenshot). This calculation is based on the centroid of each polygon. Create a new shapefile using Sort. Note that the new shapefile will have a new ...


7

The trick of remembering latitude as 'ladder'tude always helped me. Think of a ladder standing up and the rungs of the ladder representing the E-W latitude lines.


7

You can add your .dbf table into ArcMap and then create an XY event layer which you will be able to export to a shapefile. Read more details here: Adding x,y coordinate data as a layer


7

The point at (0°, 0°) is not generally given a name All geographers, cartographers and surveyors ought to know the following, but I reference some sources anyway: According to Matt Rosenberg The point at which the equator (0° latitude) and the prime meridian (0° longitude) intersect has no real significance but it is in the Gulf of Guinea in the ...


6

When someone says that data points are tiny compared to other data layers, the usual problem is that the new points have been assigned a projected coordinate system--probably the one that the other layers are using--but the new points are latitude-longitude and should be assigned a geographic coordinate system. The Add XY tool will default to the data ...


6

Here's a Python function that creates a memory layer containing a line at the specified latitude. You call it using createLatitudeLayer(latitude=-23), for example. You can specify which CRS the layer should use by specifying targetCrsEPSG=<EPSG code>. You can also specify how many points to use for creating the line, by setting numpoints=<number ...


6

Your coordinates are in UTM (Universal Transverse Mercator) Eastings and Northings. You can convert your UTM coordinates to lat/long online using many different sites. Here in one. You can also perform this calculation in excel or inside of a database if you can work out the formula. Alternatively you can perform the conversion inside of a GIS such as QGIS ...


6

From 3rd grade: lOngitude goes nOrth-sOuth


6

One could use either kind of latitude to locate points on the WGS 84 ellipsoid (used by the NED) or any other ellipsoid, but "everybody knows" that the values will always be given as geodetic latitudes. However, it is surprisingly hard to find an authoritative statement to that effect! Before we go on, it helps to understand that although a datum like the ...


6

Algorithm I use. Calculate Euclidean minimum spanning tree of points: Find 2 points most far apart from each other on this network Find shortest route between them: As one can see it might cut corner on a sharp turn. I have ArcGIS python implementation of above algorithm, it uses networkx module. Let me know if this is of interest and I'll ...


5

Assuming your data has a projected coordinate system: Set data frame to a geographic coordinate system (WGS84). Add your data. (Set datum transformation if nessesary.) Add a new field (ycoordinate). Right click field ycoordinate and calculate y-coordinate of centroid (use coordinate system of data frame for calculation.) Export data to Excel In Excel: sort ...


5

Not built in , AFAIK. The way I do this is by creating a polygon shape file "grid" and then reprojecting it. So you could: enable On-the-fly reprojection Set the CRS to Lat/Lon Use the Vector->Research Tools->Vector Grid to create a polygon grid at whatever interval is appropriate Display the polygons with no fill, to show only the grid lines. Return to ...


5

Simply create a text file with this content: id;wkt 1;LINESTRING(-180 -23, 180 -23) and use Layer -> Add delimited Text Menu entry with semicolon as delimiter and EPSG:4326 as CRS. For meridians, it is better to end the line at 89° when using EPSG:3857: id;wkt 1;LINESTRING(7 -89, 7 89)


5

Try this one: http://cs2cs.mygeodata.eu/ or use "proj" (command line below assuming UTM zone 17 south and wgs84): # geographical coordinates (ie. longitude,latitude) to utm proj -f "%.4f" +proj=utm +zone=17 +south +ellps=WGS84 < myfile # utm to geographical coordinates (ie. longitude,latitude) proj -f "%.4f" +proj=utm +zone=17 +south +ellps=WGS84 ...


5

Unless I'm misunderstanding the question, the shape's .extent property is all you need. with open('out.txt', 'wb') as out_text_file, arcpy.da.SearchCursor('path_to_data', ('msa', 'SHAPE@')) as cur: print >>out_text_file, "msa min_lon max_lon min_lat max_lat" for row in cur: msa, ext = row[0], row[1].extent print ...


5

As whuber said, they are lat-long, but in decimal minutes. Those are very uncommon, but in a sense, useful, units for geographic coords. Lat and long at Silverstone: 52.065567 and -1.020708 (decimal degrees) 3123.93402 and -61.24248 (decimal minutes) 1 degree = 60 minutes



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