7 replies to this topic

[yeneneshabebe]

Hi Dear all, I have posted this topic before but I couldn't get the exact answer up to now.
The following points shows the extent of a town which is in a local projected coordinate system ( Adindan)

X, Y (Points measurement is in meters)

LL = 489000, 1289000

UL= 489000, 1294000

UR= 495000 ,1294000

LR= 495000, 1289000

What I want is a projected coordinate system in WGS 1984 for these given points in local datum i.e Adindan. The conversion is required to purchase a high resolution satellite image for the town and the image providers want a global coordinate system (WGS 1984 projected) i.e the unit of measurement is in meters . So could any one help me on this? Thanks in advance.

[François Goulet]

I placed your coordinates on the map and it is in Ethiopia, but I have to re-ask you more information. You want the data in a projected WGS84... Like it has been said, WGS84 is a datum, not a projection.

Plate Carrée is a projection, with unit in meters and using WGS84... Mollweide too and so does the Lambert Conformal Conic and Adindan projections. For all those projections, you could have the coordinates in meters and the datum would still be WGS84.

We can't help you more than that.

Maybe you could help us by telling us who's the provider. I could help us know how you need the data.

You could also send them the coverage of the area you need... maybe they could do with that.

Attached Files

•  Coverage.zip   1.15K   19 downloads

[frax]

When we sloppily refer to wgs84, we most often refer to (at least I) equirectangular projection with decimal degrees, on the wgs84 datum (ArcInfo used to call this 'Geographic' projection, other names are 'unprojected' or 'lat/long').

[yeneneshabebe]

I placed your coordinates on the map and it is in Ethiopia, but I have to re-ask you more information. You want the data in a projected WGS84... Like it has been said, WGS84 is a datum, not a projection.

Plate Carrée is a projection, with unit in meters and using WGS84... Mollweide too and so does the Lambert Conformal Conic and Adindan projections. For all those projections, you could have the coordinates in meters and the datum would still be WGS84.

We can't help you more than that.

Maybe you could help us by telling us who's the provider. I could help us know how you need the data.

You could also send them the coverage of the area you need... maybe they could do with that.

Thank you Francois

Clearly now I understand that WGS 1984 is a datum for many projections. What I want is to convert to Transverse Mercator Projection with WGS 1984 Datum . The given points are in Transverse Mercator projection with GCS-Adindan Datum. The provider will be known after evaluation.

The other thing is how you convert this point data to polygon coverage. I have tried it many times but I couldn't get a tool which convert points to polygon in Arc GIS.

Thank you for all ur cooperation.

Edited by yeneneshabebe, 28 April 2009 - 09:22 AM.

[François Goulet]

For the area, I simply create a rectangle in Arc, and edit the localisation of each corner (with only four, It was easy and fast...).

Well then, I saved the file I sent you earlier in UTM 37N, wgs 84 and extract the corner coordinates:

UL: 489000.218124 ; 1294116.504690
UR: 495000.099147 ; 1294116.504850
LR: 495000.099062 ; 1289116.076960
LL: 489000.217936 ; 1289116.076800

You should check that I didn't make any mistake before giving it to you provider.

Good luck!

Attached Files

•  UTM37N_wgs84.zip   3.07K   17 downloads

[yeneneshabebe]

For the area, I simply create a rectangle in Arc, and edit the localisation of each corner (with only four, It was easy and fast...).

Well then, I saved the file I sent you earlier in UTM 37N, wgs 84 and extract the corner coordinates:

UL: 489000.218124 ; 1294116.504690
UR: 495000.099147 ; 1294116.504850
LR: 495000.099062 ; 1289116.076960
LL: 489000.217936 ; 1289116.076800

You should check that I didn't make any mistake before giving it to you provider.

Good luck!

Thank you very much Francois!

I posted this coordinate point as a sample. I have more than 100 data. What I have seen is, there is a significant coordinate value change (especially in the Y direction i.e 116m) in the transformed points to WGS 1984. What method you have applied to chnage the coordinate from GCS_Adindan Utm Projection to WGS 1984 UTM projection. The method I used in ARC GIs tool BOx (project tool) doesn't give different coordinate reading value. So Please tell me what procedures you followed . I am very greatful for all ur concern regarding my problems. I have got this forum very useful.

[François Goulet]

I posted this coordinate point as a sample. I have more than 100 data. What I have seen is, there is a significant coordinate value change (especially in the Y direction i.e 116m) in the transformed points to WGS 1984. What method you have applied to chnage the coordinate from GCS_Adindan Utm Projection to WGS 1984 UTM projection. The method I used in ARC GIs tool BOx (project tool) doesn't give different coordinate reading value. So Please tell me what procedures you followed . I am very greatful for all ur concern regarding my problems. I have got this forum very useful.

In ArcGIS, you probably did a "Define projection", that only tell the application that your projection is now "...". It doesn't change the values.

Would need to do a "Project" to reproject the data from your Adindan datum to UTM 37N with WGS84 datum. There's a script for "Batch project".

I didn't have to do that with a single dataset. I created the rectanble in a dataframe with the "old" projection and then, change the coordinate system of the data frame to UTM37N, wgs84. Then, I only export the data and choose "Use the same coordinate system as: the data frame". With only one or two sets of data, I prefer to do it that way.

Good luck!

[Melita Kennedy]

I posted this coordinate point as a sample. I have more than 100 data. What I have seen is, there is a significant coordinate value change (especially in the Y direction i.e 116m) in the transformed points to WGS 1984. What method you have applied to chnage the coordinate from GCS_Adindan Utm Projection to WGS 1984 UTM projection. The method I used in ARC GIs tool BOx (project tool) doesn't give different coordinate reading value. So Please tell me what procedures you followed . I am very greatful for all ur concern regarding my problems. I have got this forum very useful.

In ArcGIS, you probably did a "Define projection", that only tell the application that your projection is now "...". It doesn't change the values.

Would need to do a "Project" to reproject the data from your Adindan datum to UTM 37N with WGS84 datum. There's a script for "Batch project".

I didn't have to do that with a single dataset. I created the rectanble in a dataframe with the "old" projection and then, change the coordinate system of the data frame to UTM37N, wgs84. Then, I only export the data and choose "Use the same coordinate system as: the data frame". With only one or two sets of data, I prefer to do it that way.

Good luck!

Please see the geographic_transformations.pdf file in the Documentation folder of your ArcGIS installation. It lists the available geographic/datum transformations and their areas of interest. For example, Adindan in Ethiopia to WGS84 would use Adindan_To_WGS_1984_4.

Melita