topic Re: Data misalignment in web application in ArcGIS JavaScript Maps SDK Questions

Data misalignment in web application

SachinChand — Thu, 14 Nov 2013 14:59:48 GMT

We're having an issue where the data on a web application is not aligning correctly (see attached screenshot). We are using ArcGIS 10.2. When pulled up in the web application, however, the alignment is a bit off as seen in the screenshot. The web application uses two services, one cached and one dynamic. The misalignment is coming from the dynamic service. Any ideas on what the cause could be? I'm not a javascript/web developer so I may need a layman response 🙂

The things I've tried so far is republishing the services after upgrade to 10.2, trying several browsers and clearing browser caches. I've also verified the the issue is not with the data or the map service as the data is correct and the map service also displays with correct alignment. The projection of the map services and the web app also match.

Thank you

Re: Data misalignment in web application

JohnGravois — Thu, 14 Nov 2013 16:08:13 GMT

what are the coordinate systems (and more importantly underlying datums) of the two services?

Re: Data misalignment in web application

SachinChand — Thu, 14 Nov 2013 16:39:46 GMT

what are the coordinate systems (and more importantly underlying datums) of the two services?

Thank you for the response. Below is the coordinate system information. The application is the "Campus Place Finder" local government template from the ArcGIS Resource Center ( http://www.arcgis.com/home/item.html?id=2eb8d58bdc2246e1b101d6c01eb62023 ). We are using all ArcGIS v10.2 products and the application is v10.1. Would that be an issue?

WGS_1984_Web_Mercator_Auxiliary_Sphere
WKID: 3857 Authority: EPSG

Projection: Mercator_Auxiliary_Sphere
False_Easting: 0.0
False_Northing: 0.0
Central_Meridian: 0.0
Standard_Parallel_1: 0.0
Auxiliary_Sphere_Type: 0.0
Linear Unit: Meter (1.0)

Geographic Coordinate System: GCS_WGS_1984
Angular Unit: Degree (0.0174532925199433)
Prime Meridian: Greenwich (0.0)
Datum: D_WGS_1984
Spheroid: WGS_1984
    Semimajor Axis: 6378137.0
    Semiminor Axis: 6356752.314245179
    Inverse Flattening: 298.257223563

Re: Data misalignment in web application

JohnGravois — Thu, 14 Nov 2013 16:54:44 GMT

Sachin,

since both these coordinate systems reference the same underlying datum, no shift should be expected.

i'm not positive, but i have a hunch that at least one of the datasets in the map service which is reprojecting on the fly actually has its own differing coordinate system with different underlying datum and that no datum transformation to WGS84 was defined in the map document prior to publishing.

Re: Data misalignment in web application

SachinChand — Thu, 14 Nov 2013 17:56:54 GMT

John, thanks for the response. If that were the case, would the misalignment show up in the map service? I should also mention that the application aligning correctly. I only noticed the shift after upgrading to 10.2. It is possible the shift occurred prior to the upgrade but I only noticed it after.

Re: Data misalignment in web application

JohnGravois — Thu, 14 Nov 2013 17:58:11 GMT

how could you judge alignment until you were overlaying two different services?

i could be wrong, but i doubt that version compatibility is the problem here.

Re: Data misalignment in web application

SachinChand — Thu, 14 Nov 2013 18:02:36 GMT

how could you judge alignment until you were overlaying two different services?

i could be wrong, but i doubt that version compatibility is the problem here.

The alignment issue is on one service. The lines and polygons you see misaligned in the screenshot are from the same service. The second service is a cached basemap.

Re: Data misalignment in web application

JohnGravois — Thu, 14 Nov 2013 18:05:22 GMT

ahh! thanks for clarifying 🙂

if thats the case, the same misalignment should appear in the REST service's JavaScript Viewer and even in the map document used to publish the service.

can you confirm whether or not that is the case and check the coordinate system of the actual data?

Re: Data misalignment in web application

SachinChand — Thu, 14 Nov 2013 18:13:20 GMT

ahh! thanks for clarifying 🙂

if thats the case, the same misalignment should appear in the REST service's JavaScript Viewer and even in the map document used to publish the service.

can you confirm whether or not that is the case and check the coordinate system of the actual data?

Sorry for the confusion 🙂

The misalignments don't show up anywhere but the application. They are aligned correctly in the JS viewer and the map document. The coordinate system of the actual data is:
Projected Coordinate System: NAD_1983_StatePlane_Maryland_FIPS_1900_Feet
Projection: Lambert_Conformal_Conic
False_Easting: 1312333.33333333
False_Northing: 0.00000000
Central_Meridian: -77.00000000
Standard_Parallel_1: 38.30000000
Standard_Parallel_2: 39.45000000
Latitude_Of_Origin: 37.66666667
Linear Unit: Foot_US

Geographic Coordinate System: GCS_North_American_1983
Datum: D_North_American_1983
Prime Meridian: Greenwich
Angular Unit: Degree

Re: Data misalignment in web application

JohnGravois — Thu, 14 Nov 2013 18:45:07 GMT

are your services and/or app public?
how badly are the layers misaligned?

are you saying that both the cached basemap and dynamic map service are published in web mercator, and that your dynamic map service layers only become misaligned in that particular app?

i have a couple different suggestions.
1. compare the exportMap requests and responses for the problematic layer between the JavaScript Viewer and the Campus Viewer application to see if anything relevant seems different.
2. try defining a datum transformation between NAD83 and WGS84 in your map document prior to republishing the service.

Re: Data misalignment in web application

SachinChand — Thu, 14 Nov 2013 19:49:16 GMT

The apps and services are not public. They are misaligned by about five feet. Both services are in web mercator. The dynamic service only becomes misaligned in this app but its not used in any other apps to verify that. The service is perfectly aligned in the JS viewer. I have tried defining the datum transformation in the map document and republishing but that did not help. I have not found any discrepancies between the JS viewer and the campus app. Really bizarre!

Re: Data misalignment in web application

JohnGravois — Thu, 14 Nov 2013 20:02:01 GMT

very strange. what happens when you add the layer to the map viewer in ArcGIS online?

Re: Data misalignment in web application

SachinChand — Fri, 15 Nov 2013 13:24:15 GMT

It looks good on ArcGIS Online! I've been trying several other little things and nothing has worked. I'm going to see if I can get a developer to look at the application itself.

Re: Data misalignment in web application

SachinChand — Tue, 19 Nov 2013 20:02:55 GMT

John, your hunch of the datum transformation not being applied to the map document was correct. When I applied it after your suggestion, I applied it incorrectly (leaving out the "using" parameter). I spoke to ESRI CS and after the transformation was performed correctly, the map data aligned perfectly! Thank you for your help on this.

Re: Data misalignment in web application

JohnGravois — Tue, 19 Nov 2013 20:06:40 GMT

Sachin,
thanks for taking the time to confirm the resolution. im glad to hear the mystery is solved!

Re: Data misalignment in web application

RickeyFight — Wed, 06 Aug 2014 15:58:35 GMT

I am having the same issue. Can you remember what you did to fix the error?

Thank you

Re: Data misalignment in web application

JohnGravois — Wed, 06 Aug 2014 18:30:55 GMT

As he stated, sachin was able to resolve his problem by defining an appropriate datum transformation for layers in his map document prior to publishing his map service.

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