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8

Well, technically, NAD83 is not a subset of WGS84. If you mine further in the SpatialReference.org projetion definitions, you can see the difference between the two projections. PROJ.4 definiton of NAD83: +proj=longlat +ellps=GRS80 +datum=NAD83 +no_defs PROJ.4 definition of WGS84: +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs As you can see, the ...


6

No, a datum and ellipsoid are not equivalent. For a loose definition, think of the ellipsoid as defining size and shape. The datum then fixes that ellipsoid to the earth. NAD83 (various realizations) and WGS (another set of realizations) use almost the same ellipsoid GRS80/WGS84, and were originally designed in the 1980s to be equivalent. Since then, NAD83 ...


6

Short answer is yes. You need to convert from your coordinates' native reference frame to the NAD83 realization's reference frame, then possibly add an adjustment. In the case of NAD83(CSRS), which I use, there are 3 steps: Native RF -> ITRF96(1997.0) ITRF96 (1997.0) -> NAD83(CSRS) Grid shift Steps 1 and 2 require the Helmert transformation. Step 3 uses ...


4

WGS 1984 has had several "releases". I'm not sure whether or not to call them re-adjustments. WGS 1984 is loosely tied to the International Terrestrial Reference Frame (ITRF), maintained by IERS. The first transformation, WGS_1984_(ITRF00)_To_NAD_1983, assumes that WGS 1984 is the one tied to ITRF00 and the NAD 1983 realization is CORS96 or similar. That ...


3

You have an ESRI projection (ESRI:102719) however PostGIS (and everyone else but ESRI) are expecting EPSG:2264 (or possibly EPSG:3359 or EPSG:3632). You can use the ESRI one (just be aware that this will not interoperate well with others) - just run the following: INSERT into spatial_ref_sys (srid, auth_name, auth_srid, proj4text, srtext) values ( 9102719, ...


3

It's good practice to reproject, but not necessary, as ArcMap does reprojections on the fly. Reprojection does help to cut down on processing and server lag time, but in all cases it is not practical to reproject every time you add the layer to a map (webservices, dynamic datasets you receive from other agencies, etc). If you are in a situation where ...


2

Esri software does not have a built-in transformation to convert between NAD 1983 and NAD 1983 CSRS in Ontario. The Ontario Ministry of Natural Resources and Forestry provides an NTv2 file to convert between NAD 1983 (original) and NAD 1983 CSRS. You can download it from COSINE. You have to apply, but it's not onerous, and the NTv2 files are free to ...


2

Typically, NAD83 and WGS84 are within one meter of each other. Your concerns about differences of 2.5 feet, which are less than a meter, indicate you do need to perform this datum transformation. Briefly, this calculation requires knowledge of when the coordinates were collected so that their movement over time can be accounted for (primarily due to the ...


1

With @mkennedy's suggestion, I looked into the conversion information available within Postgis' spatial_ref_sys. The code is available in their subversion repo at http://svn.osgeo.org/postgis/trunk/spatial_ref_sys.sql The conversion statement was: TOWGS84[0,0,0,0,0,0,0] So the result of the conversion calculation was the same NAD83 values that had be ...


1

Update: I got in contact with GeoBC and they did have the NTv2 file I was looking for. Thank you!


1

I don't believe I've ever tried it but you can set the Geographic transformations in the 'Environment Settings' of the Batch Project Tool (see attached screen shot). Note: You will have to figure out which exact transformation you require (depends on the geographic area you're dealing with. The '_6' for example is for a specific region. See this page for ...


1

First, I'd like to confirm that you do have the Canadian NTv2 grid file installed (ArcGIS install, pedata\ntv2\canada\NTv2_0.gsb). To check if the data is NAD 1927, unproject it to NAD 1983. Redefine it as NAD 1927, rather than reproject it. Perhaps that's what you've done, but I'm not sure. During this process, you can also check the values in the ...


1

My guess is that the fruit data 1) has no defined coordinate reference system, 2) it's been assigned the same as the zip code data, or 3) assigned the data frame's coordinate reference system (CRS). The zip code data and the data frame may be using the same coordinate reference system. If so, it's a projected one like a UTM or State Plane zone. The fruit ...


1

It sounds like you are trying to project from NAD83 UTM Zone 12 to WGS84 UTM Zone 13N (presumably you are working on/near a zone boundary). At least in 10.1, I found WGS 1984 UTM Zone 13N under Projected Coordinate Systems>UTM>WGS84>Northern Hemisphere and I would expect it to be found in the same location at 9.3. So I think you should be able to do the ...


1

Open your file in QGIS, right click the layer and Save As... In the section labeled CRS click Browse. In the new window you can search for your desired CRS. Save your file and it will now assign the projection to your shapefile. Search didn't work, at least for me, in some earlier version of QGIS, but NAD83/Illinois East is under Projected Coord System > ...


1

I'm an Alaskan GIS user. Familiar with datums up here. Roads from AKDOT, derived from 1:63,360 scale maps, treat as "NAD83" and continue to do so, accepting NONE for transforming to other forms of NAD83 in Arc when asked. Thats because +/ 40 meter data is not at same scale as modern transforms. As for 2007, forget about it. Don't worry about that ...


1

No, you don't need to, but you will need the NTv2 transformation files for New Brunswick. They're available for download from GeoNB. The file you're interested in is NB7783v2.GSB. Once extracted from the downloaded zip file, place it in your ArcGIS home, pedata\ntv2\canada. EDIT: Okay, so most of the information above is incorrect because I assumed New ...


1

You should specify the software you are using when asking this type of question. Based on other questions I gather you are using ArcGIS, which is capable of on-the-fly reprojection. This means it will automatically reproject data to the coordinate system (CRS) of the dataframe (which either you set or is set to that of the first layer you add with a defined ...


1

Why can't you use the Field Calculator to recalculate the Lat/Long once you've done the data transformation? If you need to preserve the original values (for some reason), then add two new columns and calc those with the NAD83 values.


1

NAD1983 is a geographic coordinate system. There are a few different ways you could go about aligning these data, but I'll give an example that I think is simple and clean. (1) Add both of your CSV tables to ArcMap and plot the points. Make sure you plot them using the correct geographic coordinate system - File1(NAD1927) and File2(NAD1983). Right click the ...


1

The use of geographic vs projected is more up to you and your analysis needs. Based on what I've read so far in this question, it is not necessary for you to project into a UTM zone. However if you aren't consistent in picking the correct type of CRS, you will get alignment issues. Generally speaking (and there are exceptions) if your coordinate units are in ...



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