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Archive for the 'coordinate conversion' Category

Multiple Coordinate Systems In Google Maps, Reverse Geocoding, And More With The Worldwide Coordinate Converter

Published by
Leszek Pawlowicz
 in Google Maps, Web apps and coordinate conversion. 0 Comments

Clement Ronzon emails about his new website, The Worldwide Coordinate Converter (TWCC for short). Drag the globe-shaped icon to the desired location in a Google Maps interface, and get a pop-up balloon with the geographic coordinates for that spot, elevation in meters, and the nearest reverse-geocoded address:

twccballoon

At right is a two-part coordinates box, with latitude/longitude/WGS84 always in the top part, and a user-selectable coordinate system at the bottom:

coordschooser

You can also enter coordinates into the appropriate boxes in either the top or bottom section, click Convert, and have them converted to the other coordinate system automatically (and plotted on the map).




Look Up EPSG Codes From Well-Known-Text (WKT) / prj Files With Prj2EPSG

Published by
Leszek Pawlowicz
 in coordinate conversion. 1 Comment

OpenGeo announces Prj2EPSG, a free online service that can look up the EPSG (European Petroleum Study Group) code for a coordinate system based on:

  • A WKT (Well-Known Text) description. e,g, copying and pasting WKT text into the box:


prj2epsg




yields the EPSG code 4326.


    

  • A .prj file, often found with shapefiles or other geographic data files to define the coordinate system; select the prj file to upload, and get back the original prj data in the box and the EPSG code:
    • 



prj


    

  • Type in keywords and get back a list of possible choices:
    • 



azspcs


    

  • Or just type in the EPSG code, and get back a data page with the coordinate system defined, and the WKT listed.
    • 



Click on any of the code links in the search results to get a full data page:


prjdata


It’s kind of picky about how you describe the data, and not necessarily in a consistent fashion. For example, enter “NAD 27” and you’ll get no results, but enter “NAD27” and you’ll get results; enter “WGS84” and no results will come up, while “WGS 84” yields lots of results. Only the top 20 results display, and that’s not always enough to find what you’re looking for; there’s no option to move on to another page of results, or change the total number of results displayed. Plus, partial matches aren’t allowed; entering “SWEREF” or “SWEREF 99” yields no results, you have to specify “SWEREF99”. So for now it’s a useful adjunct to, but not yet a replacement for, the Spatial Reference website that also allows searching of the EPSG code database with keywords, and which is more flexible in matching terms (e.g. it will find just “SWEREF”). But unlike Spatial Reference, Prj2EPSG has a web service interface that allows basic search queries.


Via SlashGeo.


							
 

		
 







	
		
		

			

				
UK Coordinate Converter

				
				

					
						Published by 
Leszek Pawlowicz
					

					
						in GPS and coordinate conversion.					

					3 Comments
					
									
 
			
 

			



				
The UK’s Ordnance Survey has a free high-accuracy coordinate converter for transforming from GPS coordinates (latitude/longitude/WGS84) to OSGB National Grid (eastings and northings):


UKcoordconverter


In addition to this single-coordinate-set converter, there’s an online batch converter, and additional converter options for coordinates in the Irish Grid (good for Northern Ireland and the Republic of Ireland). There’s supposedly a free Windows stand-alone converter that you can download after filling out registration info, but the registration form doesn’t like my US phone number, so I couldn’t check it out. The OS provides both a set of equations/parameters, and a free DLL, if you want to incorporate the coordinate converter in your own software. And there’s a page with more information on coordinate systems used in Great Britain, including their free “Guide to coordinate systems in Great Britain“.


Other free services at the Ordnance Survey website include a RINEX data server for GPS post-processing, and several searchable databases of assorted geodetic control points:


    

  • 900 GPS reference marks
    • 

  • 750,000 benchmarks
    • 

  • 21,000 horizontal control stations
    • 



HT to Malc.


							
 

		
 







	
		
		

			

				
Two Online Map Scale Calculators

				
				

					
						Published by 
Leszek Pawlowicz
					

					
						in cartography and coordinate conversion.					

					0 Comments
					
									
 
			
 

			



				
With the UT-Bureau Of Economic Geology’s Scale Calculator, enter a map scale and it calculates what a measurement on the map represents in reality, or what a unit distance translates to at that map scale:


utscale


There are also links at the top of the page to other calculators for area/distance conversion, and decimal degree / deg-min-sec degree conversions (both ways).


The OSU Scale Calculator is a bit different – enter a map measurement distance for a unit distance, and get back the map scale number:


osuscale


There’s also another calculator for basic distance unit conversions, plus also conversions from degrees of slope to  % grade and back:


slopegrade


Via Kelso’s Corner (which also has some useful tables and info related to map scale),


							
 

		
 







	
		
		

			

				
The Big List Of Image Registration / Georeferencing Software

				
				

					
						Published by 
Leszek Pawlowicz
					

					
						in GIS, cartography and coordinate conversion.					

					10 Comments
					
									
 
			
 

			



				
If you want to use a raster map image in a GIS program, it needs to be calibrated so that the software will know the geographic position of every pixel in the image. This calibration data can be embedded in the file, as in GeoTiffs and MRSID files, or external as in worldfiles. If you have a raster map image which doesn’t include this calibration data, you’ll need to create it yourself; this process is called  “image registration” or georeferencing. There’s a number of free programs that can perform this function, and I’ve put together a list of some of them below; if you know of others, please let me know and I’ll add them. And if I’ve included a program that doesn’t do georeferencing (very possible, since I haven’t used all of them), let me know that as well and I’ll drop it from the list.


One thing to keep in mind: some of the programs only work correctly if the map image is already in a specific map projection like UTM or geographic, and you use the same coordinate system to georeference the image. As a general practice, it’s always best to use the same coordinate system the map was created in to georeference it. For example, if you have a map in the UTM projection, and use geographic coordinates to georeference it, the resulting calibration is unlikely to be accurate over the entire map (unless you’re at the equator). Some programs let you warp the map image to get it to match the coordinate system, a process known as “rubber-sheeting”; this is especially useful for those maps that aren’t drawn accurately, like old or hand-drawn maps, or maps created in no-longer-used coordinate systems.


BTW, I haven’t used most of these for georeferencing – GlobalMapper is my program of choice for this function. It’s not free, or even cheap, but it works great for georeferencing, including rubber sheeting. For beginners, I’d suggest looking at MapWindow, qGIS or MicroDEM first before going on to the more advanced software.


CHIPS For Windows


DIVA GIS


e-Foto


GRASS


gvSIG


HyperCube


ILWIS


Image Georeferencer


LandSerf


MapWindow


MicroDEM


MicroMSI (link may be dead)


Opticks


OSSIM


qGIS


QLandKarte


RasterStretch


Regeemy


SAGA


SavGIS


Spring GIS


TransGen


xBit


Online map rectification tools


MapWarper


Metacarta Map Rectifier


NYPL Map Rectifier


Old Maps Online Georeferencer (in development)


							
 

		
 







	
		
		

			

				
Online Coordinate Conversion And EPSG Code Lookup

				
				

					
						Published by 
Leszek Pawlowicz
					

					
						in coordinate conversion.					

					1 Comment
					
									
 
			
 

			



				
From Synectics Technical Consulting comes an Online Coordinate Reprojection System; requires installation of the Silverlight 2 platform, available for Windows/Mac/Linux. Single point conversion only, unfortunately. Select the input and output projections by clicking on the “…” button next to each setting (default is OSGB 1936 for input, WGS84 geographic for output), then enter the coordinates in the Source coords box at the left separated by a comma; multiple points can be converted by putting each set on a separate line. Make sure you’ve selected the right coordinate order for the source coordinates and destination coordinates; e.g.. the top setting (Easting,Northing) is typical for Mercator-based projections like OSGB, while the bottom is typical for geographic coordinates (lat/long):


coords


Click on “Transform”, and get the source coords re-projected; the input and output projection parameters will show up in the “Messages” box:


outputcoords


The “Swap” button swaps the input and output projection.


While probably not intended as such, you can also use this as a handy EPSG projection code lookup. Type an EPSG code into the box to the immediate right of “Projection In:” or “Projection Out:” , press the Tab key or click somewhere in the program window, and the projection corresponding to that entered code will show up to the right of it:


codelookup


If you have a projection and want the EPSG code, click on either of the “…” buttons and scroll through the list of projections; the EPSG code is conveniently listed next to each projection:


epsglookup


HT to Andrew Blake.


							
 

		
 







	
		
		

			

				
Convert/Reproject Shapefiles And KML Files To SVG Format With indiemapper

				
				

					
						Published by 
Leszek Pawlowicz
					

					
						in Web apps, coordinate conversion and shapefile.					

					Closed
					
									
 
			
 

			



				
indiemapper is a promising-looking thematic mapping service that is supposed to come online shortly. But until then, they’ve released a free  online Flash application that lets you upload vector data (point, line or polygon) in KML or shapefile format, re-project it into one of 11 different projections …


    

  • Equirectangular
    • 

  • Mercator
    • 

  • Winkel Tripel
    • 

  • Robinson
    • 

  • Albers Equal Area Conic
    • 

  • Lambert Conformal Conic
    • 

  • Orthographic
    • 

  • Polyconic
    • 

  • Sinusoidal
    • 

  • Bonne
    • 

  • Cylindrical Equal Area
    • 



… and then export it as an Scalable Vector Graphic (SVG) file for use in programs like Adobe Illustrator or Inkscape. Shapefiles must be in geographic coordinates (latitude/longitude), WGS84; KML files are already in this format. Network KML files are acceptable. Add a file to the display, or choose one or more of their sample datasets:


open


You can load multiple datasets into the display, move their draw order, and turn them on and off  by clicking on the “eye” icon:


datalayers


The graticule grid can be turned on and off, and spacing set to automatic or manual.


Select the projection using the “Project” button at upper-right:


projections


You’ll get info about the projection, including its pluses and minuses. Here’s Mercator (a screen capture, not SVG):


mercator


And Albers Equal Area Conic:


albers


With the center latitude/longitude of view adjustable. Once done, click on the “Export” button at upper right to convert the vector data to SVG format, and download it to your computer for use in vector editing software, or for viewing in a compatible browser like Firefox.


There are limitations for now. There’s no control over layer colors, and no thematic coloring based on the attributes of the vector files. It looks like the full indiemapper application will have those, and the screenshots make it look interesting, but it’s not clear yet whether that full online app will have a free version. Stay tuned.


Via the thematic mapping blog.


							
 

		
 







	
		
		

			

				
PLSS Converters For The Western United States With DLLs, Code

				
				

					
						Published by 
Leszek Pawlowicz
					

					
						in coordinate conversion.					

					Closed
					
									
 
			
 

			



				
1.  The TRS-data site at Montana State University lets you enter PLSS data (Township, Range, Section, “TRS”) for one of 17 western US states (AR , AZ, CA, CO, ID, KS, MT, ND, NE, NM, NV, OK, OR, SD, UT, WA and WY), and get back the latitude/longitude for the center of that section. You’ll need to know the correct meridian for the TRS section you’re interested in; the same site has a map that you can click on that will bring up a datasheet with the meridian. It also will give you information about the point you clicked on like latitude/longitude, slope, aspect, roughness, nearby landmarks,etc., but the scale of the map is so small that most of this data isn’t terribly useful.


2. The site above uses Martin Wefald’s free TRS converter software, available for free download. This includes a DOS executable, DLLs for use in other Windows programs (including both TRS to lat/long and lat/long to TRS), source code, documentation and a sample Visual Studio app for TRS to lat/long conversion that functions similarly to the above website:


trs2ll


3. Paul Jorgensen has used these DLLs to create more stand-alone converters:


- A single-point app for converting TRS to lat/long, or vice-versa:


trs


- A bulk converter that takes a text file with TRS data, and outputs a text file with lat/long data. Documentation and download at this website. The format the input data needs to be in is very specific, so it might not be the easiest to work with.


4. While I’m on the topic: I’ve posted before about the Township And Range website, which takes TRS data and plots the location in Google Earth. Since the original post date, the author has added converters that will take TRS data and convert it to lat/long, and vice-versa, with the option to view the location immediately in Google Earth.


HT to Steve Richardson.


							
 

		
 







		
		
	


			
	

			
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