I have a small section of point cloud on MGA55 projection.
I converted it to a new las file on EPSG 7855 using las2las from the LASTools suite.
I then uploaded the 2 files to Cesium and I am seeing a difference or around 1.8m cloud to cloud.
I have interrogated the 2 files in CloudCompare to see that the file contents has not changed. They do not, they overlay perfectly.
The only thing about the 2 las files that I can see that is different is that the projection information in the las header and the variable length records has changed after the conversion, which I would assume is entirely to be expected.
I cannot figure out why this reprojection is not mapping perfectly, any ideas?
I guess the difference comes from
the conversion from MGA55 to ECCF and the conversion from EPSG 7855 to ECCF.
I have found the issue, I believe the tool set I am using is reprojecting to an old datum:
"The Geocentric Datum of Australia 2020 (GDA2020) is Australia’s new national datum which replaces GDA94. GDA2020 is of higher-accuracy than GDA94, aligns more closely with GPS and GNSS positioning services and supports nationally consistent datasets, free of the known distortions of GDA94. GDA2020 coordinates are approximately 1.8 metres to the north east of GDA94 coordinates, which represents the tectonic motion of the Australian plate between 1994 and 2020."
My errors align with the rough bearing and distance indicated by this post.
Related
I'm looking for some guidance on the approach I should take to mapping some points with R.
Earlier this year I went off to a forest to map the spatial distribution of some seedlings. I created a grid—every two meters I set down a flag with a tagname, and what I did is I would measure the distance from a flag to a seedling, as well as the angle using a military compass. I chose this method in hopes of getting better accuracy (GPS Garmins prove useless for this sort of task under canopy cover).
I am really new to spatial distribution work altogether, so I was hoping someone could provide guidance on what R packages I should use.
First step is to create a grid with my reference points (the flags). Second step is to tell R to use a reference point and my directions to mark the location of a seedling. From there come other things, such as cluster analysis.
The largest R package for analysing point pattern data like yours is spatstat which has a very detailed documentation and an accompanying book.
For more specific help you would need to upload (part of) your data so we can see how it is organised and how you should read it in and convert to standard x,y coordinates.
Full disclosure: I'm a co-author of both the package and the book.
I have some coordinate data and the only thing i know about its coordinate system is the
following description:
PROJCS["Basic Albers NAD83",
GEOGCS["GCS_North_American_1983",
DATUM["D_North_American_1983",
SPHEROID["GRS_1980",6378137.0,298.257222101]
],
PRIMEM["Greenwich",0.0],
UNIT["Degree",0.0174532925199433]
],
PROJECTION["Albers"],
PARAMETER["False_Easting",0.0],
PARAMETER["False_Northing",0.0],
PARAMETER["Central_Meridian",-96.0],
PARAMETER["Standard_Parallel_1",45.5],
PARAMETER["Standard_Parallel_2",29.5],
PARAMETER["Latitude_Of_Origin",23.0],
UNIT["Foot_US",0.3048006096012192]
]
this comes from a prj arcGis file.
I need to convert from this system to GPS (Google maps) system and vice-versa.
this must be done programatically and i cannot use esri libraries (license issues)...
Could you explain the meaning of all these parameters?
are the coordinates expressed in the spheroid and the projection (albers) used only when drawing
the map? or the coordinates depend on the projection used also?
Do you know an open source library I could use for this transformation?
Thanks!
All these parameters define the projection, including:
Projection type (Albers)
GEOGCS defines the geoid (idealized Earth shape) used by the project. In this case, it's NAD83, which uses degrees for units and is centered at the Greenwich, the 0th longitude.
Where the projection itself is centered
How far the projection is moved north and east to make any negative coordinates
positive (False Easting and False Northing)
Units for coordinates in this projection (US Feet)
Some other information about how coordinates of the projection were transformed to be drawn on a flat service.
I have a blog post which goes over the details for an OGC WKT definition, which is very similar to the content in an ESRI .prj file: http://www.dev-garden.org/2011/07/30/projections-for-programmers-one-projection/. You may find it useful.
With projected coordinates, they have already been 'drawn on the map', and you need to reproject them to use in other coordinate systems like Google's projection.
There are many open source tools you can use to reproject your coordinates from one projected system to another. Here are a few:
Geotools or Proj4j - Java
Proj4js - Javascript
Proj - C or C++
dotspatial - C#
One command line tool I find very useful is ogr2ogr. Using ogr2ogr, it is very easy to reproject coordinates from one system to another. Here's how to convert a projected shapefile to a Google Earth projection:
ogr2ogr -f "ESRI Shapefile" -t_srs EPSG:3857 NEWFILE.shp OLDFILE.shp
Ogr2ogr uses the .prj file to determine the current projection of the shapefile, and then reprojects it to Googles projection, defined here by the EPSG shorthand EPSG:3857. You can find ogr2ogr for Windows and other platforms at http://fwtools.maptools.org/
I'm working on a GeoTargeting application. I'm curious if longitude and latitude of a point on the earth can change?
If you know the exact position of the statue of liberty how sure is it that longitude and latitude will stay the same.
Does it change according to the season, time in the year, or slowly over time
Wikipedia to the rescue:
The surface layer of the Earth, the
lithosphere, is broken up into several
tectonic plates. Each plate moves in a
different direction, at speeds of
about 50 to 100 mm per year. As a
result, for example, the longitudinal
difference between a point on the
equator in Uganda (on the African
Plate) and a point on the equator in
Ecuador (on the South American Plate)
is increasing by about 0.0014
arcseconds per year.
It depends on the map projection variables you use. Currently WGS-84 is used mostly.
The same point can have different coordinates depending on the variables. They do not differ a lot, I remember the difference between EUR-50 (or something like that) and WGS-84 was at most 50 meters or something.
You're tangentially referring to geodetics, which is the science of modelling (representing) the shape of the earth. So while a physical location may not change, the datum (model) used by a geodetic coordinate system will change, fortunately this does not happen frequently.
In North America NAD83 is the mostly widely used datum, which replaced NAD27.
Did I mention that Geographic Information Systems (GIS) was my foray into software development?
Yes. Zip codes get split all the time, and doing so would move the center of the zip code to a new location.
47.554 always equals 47.554
But if the shape of the earth changes or you are using different methods of calculations (there are plenty) or if the input data changes in precision or if if your compiler treats floating point differently..
you'll end up in different long/lat
I have a set of ESRI shapefiles which, I'm told, have been written using the British National Grid coordinate system. I need to convert these files to WGS84 lat/lons, for onward conversion to KML files. I'm having trouble doing this as follows:
If I open each of the original files in MapInfo Professional telling it that my file has a projection which is British National Grid then I can't see any geographic objects in the file; the map window is completely empty.
If I use MapInfo Professional's Universal Translator to convert the files to a WGS84 MapInfo TAB file then, just as before, the converted file won't display any geographic objects, the MapInfo window is empty.
Can I verify the coordinate system of these files? Am I missing anything here? Should I be able to convert the shapefiles in the way I'm expecting to be able to and view them using MapInfo Professional? Will another tool do a better job for me?
Thanks.
More Info:
My shapefile has coordinates which don't seem to translate to lat/lon properly and I'm now wondering if the coordinates aren't actually British National Grid. I'm seeing coordinates such as 383702523, 399081141 which appears to be approximately lat/lon 53.488182, -2.247153. Have you any idea what projection system my input file is in?
OS grid doesn't use WGS84 - it uses Airy 1936 (OSGB36) spheroid
So you need to go from OSgrid -> lat/lon then OSGB36->WGS84.
See http://www.ordnancesurvey.co.uk/oswebsite/gps/docs/convertingcoordinatesEN.pdf
To do OS grid to lat-lon see http://www.movable-type.co.uk/scripts/latlong-gridref.html
Then to go from OSGB36 -> WGS84 see http://www.movable-type.co.uk/scripts/latlong-convert-coords.html
http://gothos.info/2009/04/14/transform-projections-with-gdal-ogr/
ogr2ogr is a great tool for doing these sorts of conversions. You would run it with a command like
ogr2ogr -t_srs EPSG:4326 map_wgs84.shp map_original.shp
-t_srs is the option to transform co-ordinate systems. 4326 is the EPSG SRID for WGS84.
I'm working on a project that contains Thomas Brothers Map page and grid numbers. Is there a way to programatically convert from this map page to a latitude & longitude?
An Example would be for the intersection of the US101 & I405 freeways.
ThomasBrothers: 561-3G (page-grid)
Not that I know of, but I don't have a lot of experience with Thomas bros maps. Are you talking about printed version of the maps or is there a link somewhere to an online map?
If you just need a few lat/longs, then you can look up the locations that correspond to the grid and get the lats and longs manually at many websites, including http://itouchmap.com/latlong.html
If you provide a link to a Thomas bros map that you are using, I might be able to help further.
By looking at the link above, you can determine that US 101 and I-405 has a latitude of 34.16073390017978 and a longitude of -118.46952438354492.
Your best source would be the map publisher. If they choose to help, someone there can tell you exactly what you need to know. If they won't help you, it's unlikely that they've released the information to anyone else.
If that's the case, you could do some work by hand to correlate one point from the map grid to your target coordinate system. Effectively, you could reverse engineer a mapping "datum" for each page. You'd also have to know what map projection was used to render the maps, so that you can calculate the transform from the map coordinates to the geographic coordinates as you move away from your "origin". Finally, you'll need to establish the orientation of the map, since different notions of "north" exist.
It sounds like the Thomas maps use a new grid for every page, rather than bleeding the grid continuously from page to page. If that's the case, you'll have to correlate one point on each map. For example, find a spot where a map grid intersection coincides with a notable road intersection. Then you can find the coordinates of the road intersection using a map with latitude and longitude (a topographic map, TerraServer, etc.). Doing this with two points on the same vertical grid line should help you establish the north used on the map as well.
The short answer is that each of the nine regions has a grid derived from a Lambert conformal conic projection with custom parameters, so you cannot write a conversion program without the parameters.
I've also got ThomasBros. pages that I would like to convert to lat/long for lookup against Google Maps API. They also provided something called TBXY ... not sure what this is -- perhaps some notation for GPS/lat/long?
<Area>"El Cajon"</Area>
<ThomasBrothers>"1297 5E"</ThomasBrothers>
<TBXY>"6481390:1827008"</TBXY>
Thomas Brothers Maps invested a lot when developing their GIS system to create their digital mapping system. Though the first "digitally produced" map was Sacramento County-1990, the development began back in 1986. I expect that their map projection equations are a well guarded trade-secret, which Rand McNally now owns. I'd don't know those equations, but would also like to know them.
There are 9 projections covering the 48 states. If you know the equations for Los Angeles, it is valid across California & Nevada. Oregon & Washington have their own projection. Arizona, New Mexico, Colorado, and Utah share another projection.
I do know this...
As many know, the page grid is an exact 1/2 mile square, or 2640 feet by 2640 feet. The coordinate measurement unit is 1 foot.
To determine the Thomas Brothers XY Coordinate, get one or more of the Thomas Guide CD- ROM maps, which were recently discontinued. The last ones produced for certain California counties were the 2008 edition. Last editions for Seattle, Portland, Las Vegas, and Phoenix/Tucson were the 2007 edition. Each is still available on the Rand McNally website for $20.
When you geo-code a group of addresses, you'll see an output file with the TGXY coordinates and Lat/Lon for the addresses you specified, and the page # and grid that point is in. Once that file is open, you can click on the map to add additional geo-coded points, which will also provide both the coordinates. The output file is saved in an Access database ".mdb" file.
If you know a lot about map projections or solid geometry, the set of corresponding TGXY and Lat/Lon coordiantes will provide you some good data for testing.
As you mentioned San Diego Page 1297, I'll provide its bordering coordinates.
West x=3062760
East x=3086520
North y=0985040
South-y=0966560
This is not in range of the "TBXY" you found on Google. Maybe it's the same projection, with a relocated origin.