[MetaCRS] Followup: RE: MetaCRS Digest, Vol 28, Issue 6
Ben Krepp
bkrepp at ctps.org
Mon Sep 20 15:31:02 EDT 2010
Thanks to Mike Adair for diagnosing the root cause of the problem I was
running into.
I had an incorrect definition of the EPSG:4326 projection in my JavaScript
source. For whatever reason, a definition of this projection wasn't included
in the copy of Proj4js I downloaded. A (correct) one has been placed there,
and all is now well.
--- Ben
-----Original Message-----
From: Mike Adair [mailto:madair at dmsolutions.ca]
Sent: Monday, September 20, 2010 12:18 PM
To: Ben Krepp
Subject: Re: [MetaCRS] Followup: RE: MetaCRS Digest, Vol 28, Issue 6
Ben,
I think you may have posted that last question to the list anyway. I
suspect your problem is when you redefine the EPSG:4326 projection with a
new ellipse and datum transformation. That one should be:
Proj4js.defs["EPSG:4326"] = "+proj=longlat +ellps=WGS84 +datum=WGS84
+no_defs";
and it is already defined by default in Proj4js so take out the definition
you have.
The answers to you other questions:
- there is a test page in the test subdirectory, you can put a known lat/lon
and x/y pairs in the file testdata.js (comment out all other points). Then
loading the page will compare the known point with the generated one. You
should also be able to just add the Proj4js.defs value in the main index
page and it should show up in the drop down then.
- the latest release is 1.0.1; a 1.0.2 version is close but there would be
no changes affecting your transformation
Mike
On 9/20/2010 11:47 AM, Ben Krepp wrote:
> Hi Mike,
>
> Thanks very much for chiming in on my question to the MetaCRS mailing
list.
> I'm writing back to you directly, rather than via the mailing list, in
order
> to minimize "chatter" for others on the list. When the issue I'm running
> into is resolved, I'll post the results back to the list.
>
> To answer the question you ask in your reply:
> es, I'm using exactly the same initialization string as the one you quoted
> in your message. I'll post the full text of my code (which I've whittled
> down to a pretty minimal test case) at the bottom of this message. It can
> also be viewed "live" at http://www.bostonmpo.org/apps/bktest/test.js ;
the
> page that loads my test code can also be viewed "live", at:
> http://www.bostonmpo.org/apps/bktest/test.cfm (The somewhat funny looking
IF
> statement in test.cfm can be ignored - it's simply selecting which of the
> two Google Maps keys we have to use, depending on the server).
>
> In any case, the long and the short of it is, I'm doing the following
>
> 1. Initializing Proj4js.defs for EPSG:4236 and EPSG:26986
> 2. Creating Proj4js.Proj objects for these two projections
> 3. Initializing a Proj4js Point object with the EPSG:4236 coordinates of
the
> point
> 4. Calling Proj4js.transform do to the EPSG:4236 to EPSG:26986
> transformation
> 5. Printing out the coordinates of the 'transformed' point
>
> A couple of follow up questions:
>
> 1. I'm using version 1.0.1 of proj4js, the most recent one I'm aware of. I
> downloaded it http://trac.osgeo.org/proj4js/wiki/Download. Are you using
a
> more recent version? If so, what is it, and where can I obtain it?
> 2. In your message, you mention that you transformed my point in the
Proj4js
> test page. When I took a look at the Proj4js test page
> (http://www.proj4js.org/), EPSG:26986 isn't available as a 'dest' spatial
> reference. Are you referring to a different Proj4js test page? If so, can
> you point me to it?
>
> One other point: I'm a new user of Proj4js, and am following the
> instructions posted in the on-line User Guide
> (http://trac.osgeo.org/proj4js/wiki/UserGuide). In my first cut at this
> little app, I put
> <scrip! src="../proj4js/lib/defs/EPSG4236.js"
> type="text/javascript"> </script> and
> <scrip! src="../proj4js/lib/defs/EPSG26986.js"
> type="text/javascript"> </script> tags in my test.cfm file.
> However, I later noticed that these files were not present in the copy of
> Proj4js that I downloaded, and I switched to putting the initialization
code
> in-line, as was the case in the example in your message.
>
> I'm still getting transformed coordinates that are off by a couple of
> hundred meters (no change from Friday). So, it's clear that I'm not able
> reproduce the (correct) behavior that you are seeing.
> Any tips/thoughts on what I might be doing wrong or what might be going
> wrong on my end would be much appreciated.
>
> Thanks very much, and best regards,
> Ben
> Ben
>
> //////////////// Begin included source code //////////////////////////
> CTPS = {};
> CTPS.testApp = {};
>
> // Initialization for Proj4js
> // Google Maps LatLon SRS
> Proj4js.defs["EPSG:4236"] = "+proj=longlat +ellps=intl
> +towgs84=-637,-549,-203,0,0,0,0 +no_defs";
> // Mass State Plane NAD83 meters SRS
> Proj4js.defs["EPSG:26986"] = "+proj=lcc +lat_1=42.68333333333333
> +lat_2=41.71666666666667 +lat_0=41 +lon_0=-71.5 +x_0=200000 +y_0=750000
> +ellps=GRS80 +datum=NAD83 +units=m +no_defs";
>
> // Error reporting function for Proj4js
> Proj4js.reportError = function(msg) {
> alert("Proj4js error: " + msg);
> }
>
> CTPS.testApp.load = function() {
> if (GBrowserIsCompatible()) {
> var map = new GMap2(document.getElementById("map"));
> // Define Google Maps LatLng point for the location of the
> Harvard Square MBTA station.
> var oGoogleLatLng = new
> GLatLng(42.37346263960867,-71.11881762742996);
> map.setCenter(oGoogleLatLng, 19);
> map.addControl(new GSmallMapControl());
> map.addControl(new GScaleControl());
> map.addControl(new GMapTypeControl());
> map.setMapType(G_SATELLITE_MAP);
> } else {
> alert("Your browser doesn't support Google Maps.");
> return;
> }
>
> // 'Source' SRS: Google Maps Lat/Lon
> var oSrcPrj = new Proj4js.Proj('EPSG:4236');
> // 'Destination' SRS: Massachusetts State Plane NAD83, meters
> var oDestPrj = new Proj4js.Proj('EPSG:26986');
> // Define Proj4js point for location of the Harvard Square
MBTA
> station.
> var oPoint = new Proj4js.Point(oGoogleLatLng.x,oGoogleLatLng.y);
> // Project from EPSG:4236 to EPSG:26986; the projection is done
> 'in place.'
> Proj4js.transform(oSrcPrj,oDestPrj,oPoint);
> alert("Transformed LatLng->MassStatePlane coordinates are: X = " +
> oPoint.x + " Y = " + oPoint.y);
> }
> //////////////////// End included source code //////////////////////////
>
>
> -----Original Message-----
> From: metacrs-bounces at lists.osgeo.org
> [mailto:metacrs-bounces at lists.osgeo.org] On Behalf Of
> metacrs-request at lists.osgeo.org
> Sent: Saturday, September 18, 2010 12:00 PM
> To: metacrs at lists.osgeo.org
> Subject: MetaCRS Digest, Vol 28, Issue 6
>
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>
>
> Today's Topics:
>
> 1. Proj4js problem: EPSG:4236 to EPSG:26986 transformation
> (Ben Krepp)
> 2. Re: Proj4js problem: EPSG:4236 to EPSG:26986 transformation
> (Mike Adair)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 17 Sep 2010 15:19:41 -0400
> From: "Ben Krepp"<bkrepp at ctps.org>
> Subject: [MetaCRS] Proj4js problem: EPSG:4236 to EPSG:26986
> transformation
> To:<metacrs at lists.osgeo.org>
> Message-ID:<00dd01cb569d$470c3e30$d524ba90$@ctps.org>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi all,
>
>
>
> I'm trying to use the Proj4js library to transform coordinates from the
> Google Maps SRS (EPSG:4236) to the Massachusetts State Plane NAD83 meters
> SRS (EPSG:26986) SRS, but am running into problems. Specifically, the
> results I'm getting are off by a several hundred meters for both the X and
Y
> values.
>
>
>
> The following snippet of JavaScript code is sufficient to expose the
issue:
>
>
>
> // Begin code snippet
>
> var oSrcPrj = new Proj4js.Proj('EPSG:4236');
>
> var oDestPrj = new Proj4js.Proj('EPSG:26986');
>
> var oPoint = new
> Proj4js.Point(-71.11881762742996,42.37346263960867);
>
> Proj4js.transform(oSrcPrj,oDestPrj,oPoint);
>
> alert("Transformed LatLng->MassStatePlane coordinates
are: X
> = " + oPoint.x + " Y = " + oPoint.y);
>
> // End code snippet
>
>
>
> The oPoint variable represents the location of the Harvard Square MBTA
> station in Cambridge, MA., as reported by Google Maps .The coordinate
values
> were obtained by printing them out in a simple Google Maps onclic! event
> handler.
>
>
>
> When run, the coordinates of the transformed point are:
>
> X = 230616.5448393133, Y = 902165.5744436784
>
>
>
> According to the MassGIS MBTA_NODE GIS layer, which uses the Massachusetts
> State Plane NAD83 meters (i.e., EPSG:26986) SRS, the coordinates of this
> point are:
>
> X = 231394.7344, Y = 902622.1875
>
>
>
> So, there is a large discrepancy between the actual and expected results.
>
> Am I using the library incorrectly, or is there a bug in Proj4js?
>
>
>
> Thanks for any light that can be shed on this.
>
>
>
> Ben Krepp
>
> Manager of Information Technology, GIS, and Data Services
>
> Central Transportation Planning Staff
>
> 10 Park Plaza
>
> Suite 2150
>
> Boston, MA 02115
>
> e-mail: bkrepp at ctps.org
>
> phone: 617-973-7137
>
>
>
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> ------------------------------
>
> Message: 2
> Date: Fri, 17 Sep 2010 15:44:42 -0400
> From: Mike Adair<madair at dmsolutions.ca>
> Subject: Re: [MetaCRS] Proj4js problem: EPSG:4236 to EPSG:26986
> transformation
> To: metacrs at lists.osgeo.org
> Message-ID:<4C93C52A.7080301 at dmsolutions.ca>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Ben,
>
> Running that point in the test page of Proj4js, I get:
> 231394.84, 902621.11
> (which is also almost exactly the same result I get from PROJ.4) and off
> from your expected result by centimeters.
>
> Are you using the correct initialization string?
>
> Proj4js.defs["EPSG:26986"] = "+proj=lcc +lat_1=42.68333333333333
> +lat_2=41.71666666666667 +lat_0=41 +lon_0=-71.5 +x_0=200000 +y_0=750000
> +ellps=GRS80 +datum=NAD83 +units=m +no_defs";
>
> (also at http://spatialreference.org/ref/epsg/26986/proj4js/)
>
> Mike
>
>
> On 9/17/2010 3:19 PM, Ben Krepp wrote:
>> Hi all,
>>
>> I'm trying to use the Proj4js library to transform coordinates from
>> the Google Maps SRS (EPSG:4236) to the Massachusetts State Plane NAD83
>> meters SRS (EPSG:26986) SRS, but am running into problems.
>> Specifically, the results I'm getting are off by a several hundred
>> meters for both the X and Y values.
>>
>> The following snippet of JavaScript code is sufficient to expose the
>> issue:
>>
>> // Begin code snippet
>>
>> var oSrcPrj = new Proj4js.Proj('EPSG:4236');
>>
>> var oDestPrj = new Proj4js.Proj('EPSG:26986');
>>
>> var oPoint = new
>> Proj4js.Point(-71.11881762742996,42.37346263960867);
>>
>> Proj4js.transform(oSrcPrj,oDestPrj,oPoint);
>>
>> alert("Transformed LatLng->MassStatePlane coordinates
>> are: X = " + oPoint.x + " Y = " + oPoint.y);
>>
>> // End code snippet
>>
>> The oPoint variable represents the location of the Harvard Square MBTA
>> station in Cambridge, MA., as reported by Google Maps .The coordinate
>> values were obtained by printing them out in a simple Google Maps
>> onclic! event handler.
>>
>> When run, the coordinates of the transformed point are:
>>
>> X = 230616.5448393133, Y = 902165.5744436784
>>
>> According to the MassGIS MBTA_NODE GIS layer, which uses the
>> Massachusetts State Plane NAD83 meters (i.e., EPSG:26986) SRS, the
>> coordinates of this point are:
>>
>> X = 231394.7344, Y = 902622.1875
>>
>> So, there is a large discrepancy between the actual and expected results.
>>
>> Am I using the library incorrectly, or is there a bug in Proj4js?
>>
>> Thanks for any light that can be shed on this.
>>
>> Ben Krepp
>>
>> Manager of Information Technology, GIS, and Data Services
>>
>> Central Transportation Planning Staff
>>
>> 10 Park Plaza
>>
>> Suite 2150
>>
>> Boston, MA 02115
>>
>> e-mail: bkrepp at ctps.org<mailto:bkrepp at ctps.org>
>>
>> phone: 617-973-7137
>>
>>
>> _______________________________________________
>> MetaCRS mailing list
>> MetaCRS at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/metacrs
--
Michael Adair
Senior Software Architect
DM Solutions Group Inc.
Office: (613) 565-5056 x26
madair at dmsolutions.ca
http://www.dmsolutions.ca
http://research.dmsolutions.ca
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