topic Re: UTM to Latitude and Longitude in ArcGIS API for Silverlight Questions

UTM to Latitude and Longitude

MichaelAquilina — Sat, 14 May 2011 17:06:34 GMT

Hi everyone, id really appreciate some help understanding how to place the data in these shape files onto the ArcGIS control. The values are in utm but the ArcGIS control with Bing Imagery uses Web Mercator (i assume these are not the same?)

Also, is there some form of way of placing objects over the map without using a canvas?

Thanks in Advance!

Re: UTM to Latitude and Longitude

IgressT — Sun, 15 May 2011 17:25:35 GMT

Hi everyone, id really appreciate some help understanding how to place the data in these shape files onto the ArcGIS control. The values are in utm but the ArcGIS control with Bing Imagery uses Web Mercator (i assume these are not the same?)

Also, is there some form of way of placing objects over the map without using a canvas?

Thanks in Advance!

There might a better way but I did the same kind of thing in my current project by using the geometry service.
The service has a Project method that accepts list of graphics that needs to be projects along with in spatial reference and out spatial reference.

Re: UTM to Latitude and Longitude

MichaelAquilina — Sun, 15 May 2011 18:13:00 GMT

There might a better way but I did the same kind of thing in my current project by using the geometry service.
The service has a Project method that accepts list of graphics that needs to be projects along with in spatial reference and out spatial reference.

Hi and thanks for your reply

I have found out how to add items over the map, however i am now having some difficulty with projections. I am trying to get to place TIGER road vector data over the ArcGIS control which is using Bing Aerial Imagery. I am using GeographicToWebMercator() on each point found in the shape file to convert it from unprojected lat long to mercator projection, however this is horribly displaced and wont be of much use this way. Is there some better method that i am not aware of? Or is it something i cannot avoid?

I am using to data found on ArcGIS site:
http://arcdata.esri.com/data/tiger2000/tiger_download.cfm

Re: UTM to Latitude and Longitude

DominiqueBroux — Mon, 16 May 2011 06:39:37 GMT

From your first post, the coordinates are in UTM. In this case GeographicToWebMercator doesn't help and the only option is the geometry server (or to write by yourself the conversion code at the client side)

Re: UTM to Latitude and Longitude

MichaelAquilina — Mon, 16 May 2011 08:24:39 GMT

From your first post, the coordinates are in UTM. In this case GeographicToWebMercator doesn't help and the only option is the geometry server (or to write by yourself the conversion code at the client side)

Hi, it is true that in my first post i was using data in UTM, however i have now changed to using TIGER vector data which seems to be in unprojected latitude and longitude (see the link i sent).

I cant seem to find this geometry server, is it in the library reference? How and what exactly is it used for? Sorry for my lack of knowledge in this area, but im still kind of new 😕

Thanks!

Re: UTM to Latitude and Longitude

DominiqueBroux — Mon, 16 May 2011 11:25:43 GMT

There is a sample on how to use a geometry server for projecting coordinates : http://help.arcgis.com/en/webapi/silverlight/samples/start.htm#Project

But, if your coordinates are geographical, you should not need a geometry server. 'GeographicToWebMercator' should work.
Try debugging the input and the output values of GeographicWebMercator. This could give a clue.

For example, it might happen that the coordinates are reversed (Latitude/Longitude instead of Longitude/Latitude).

Re: UTM to Latitude and Longitude

MichaelAquilina — Mon, 16 May 2011 14:25:31 GMT

There is a sample on how to use a geometry server for projecting coordinates : http://help.arcgis.com/en/webapi/silverlight/samples/start.htm#Project

But, if your coordinates are geographical, you should not need a geometry server. 'GeographicToWebMercator' should work.
Try debugging the input and the output values of GeographicWebMercator. This could give a clue.

For example, it might happen that the coordinates are reversed (Latitude/Longitude instead of Longitude/Latitude).

well thats the method im using for converting the values and it still seems to give me offset results. The shape and topology of the vectors are correct but they do not "align" well with the imagery which gives me the impression i am doing something wrong in terms of a projection.

Could someone do me a huge favor and confirm for me whether the coordinates used in the TIGER files are geographic coordinates? Are they stored under some projection that i am no aware of? ( i cant seem to find a .prj file with the shape files so i assumed they were unprojected)

Re: UTM to Latitude and Longitude

IgressT — Mon, 16 May 2011 14:34:03 GMT

well thats the method im using for converting the values and it still seems to give me offset results. The shape and topology of the vectors are correct but they do not "align" well with the imagery which gives me the impression i am doing something wrong in terms of a projection.

Could someone do me a huge favor and confirm for me whether the coordinates used in the TIGER files are geographic coordinates? Are they stored under some projection that i am no aware of? ( i cant seem to find a .prj file with the shape files so i assumed they were unprojected)

If its of any help you have to DEFINE a projection to the Tiger files before using them.

Re: UTM to Latitude and Longitude

MichaelAquilina — Mon, 16 May 2011 16:31:45 GMT

If its of any help you have to DEFINE a projection to the Tiger files before using them.

wouldnt making use of the GeographicToWebMercator() method handle this on its own?

Re: UTM to Latitude and Longitude

DominiqueBroux — Tue, 17 May 2011 07:35:28 GMT

At this time, my best bet is still that you reversed the coordinates (Latitude/Longitude instead of Longitude/Latitude).
Did you check this point?

Can you share how look the input coordinates when you call 'GeographicToWebMercator'?

Re: UTM to Latitude and Longitude

MichaelAquilina — Sat, 11 Dec 2021 07:03:58 GMT

At this time, my best bet is still that you reversed the coordinates (Latitude/Longitude instead of Longitude/Latitude).
Did you check this point?

Can you share how look the input coordinates when you call 'GeographicToWebMercator'?

This is the code i am using to place the coordinates on the screen. The ShapeFile class was implemented by myself and basically loads the data into appropriate shapes. In this case we are dealing with PolyLines so i iterate through the coordinates in each polyline and transform them with the GeographicToWebMercator().

ShapeFile File = new ShapeFile();
            File.Read(ShapeFile);

            int count = 0;

            foreach (PolyLine Line in File.Data)
            {
                count++;
                Polyline Polyline = new Polyline();

                for (int i = 0; i < Line.NumParts; i++)
                {
                    int End = (i == Line.NumParts - 1) ? Line.NumPoints : Line.Parts[i + 1];
                    PointCollection Collection = new PointCollection();

                    for (int j = Line.Parts; j < End; j++)
                    {
                        MapPoint GeographicPoint = new MapPoint(Line.Points.X, Line.Points.Y);
                        Collection.Add(GeographicPoint.GeographicToWebMercator());
                    }
                    Polyline.Paths.Add(Collection);
                }
                AddToMap(Polyline);
            }

I do not think i am swapping the two coordinates because the data itself follows the same shape but is displaced and skewed. Its for this reason that i suspect it has to do with a map projection. I have included images as well to show what i am refering to:

Notice how it is not simply the case that the positions are offset by a constant X,Y amount, but rather the lines are simply distorted as if they have been affected by a map projection.

Could it be that the TIGER data i am using simply isnt good for use with Bing's Imagery?

Re: UTM to Latitude and Longitude

MichaelAquilina — Wed, 18 May 2011 12:23:49 GMT

Anyone?

sorry for the large images by the way, but i cant seem to find the edit button on my post :S

Re: UTM to Latitude and Longitude

DominiqueBroux — Wed, 18 May 2011 12:40:19 GMT

At this time, my best bet is still that you reversed the coordinates (Latitude/Longitude instead of Longitude/Latitude).

Seeing the screenshot, I lost my bet for sure:o

but rather the lines are simply distorted as if they have been affected by a map projection.

At this scale, I don't think the map projection can explain the distorsion. Likely a data accuracy matter.

Notice how it is not simply the case that the positions are offset by a constant X,Y amount

Yeah. Accuracy of data or projection issue (not the same spheroid?) ? I will avoid to lose a second bet on that question:).

Re: UTM to Latitude and Longitude

LanceCrumbliss — Wed, 18 May 2011 13:30:19 GMT

At this scale, I don't think the map projection can explain the distorsion. Likely a data accuracy matter.

yeah, i'm going to have to agree with dbroux; TIGER data is notoriously inaccurate at such scales.

Re: UTM to Latitude and Longitude

MichaelAquilina — Wed, 18 May 2011 16:38:28 GMT

Thanks for all the replies, all very helpful! 🙂

would anyone of you happen to know of freely available shapefiles that contains US road data then?

I need the data to be accurate enough to use as a reference inevaluation (which means i definitely cannot use the data found in the TIGER shapefiles)