topic Re: Homogenisation in 911 GIS Questions

Homogenisation

TheresaFurness — Thu, 27 Apr 2017 09:35:22 GMT

Hi,

I am new to ArcGIS. I am a bit stuck. I am adding a 2 layers in ArcMap :

ArcGIS coordinate system

* Type Geographic

* Geographic coordinate reference GCS_WGS_1984

and

* Type Projected

* Geographic coordinate reference GCS_MGI

* Projection MGI_Austria_GK_M31

I cannot see the projected layer - when I Define Projection as MGI, they are both there, but very FAR apart. Is it the Datum that is incorrect? How can I correct this?

Thanks in advance

Terri

Re: Homogenisation

DanPatterson_Retired — Thu, 27 Apr 2017 09:43:05 GMT

You don't define a projection unless the file is actually in that coordinate system, so check the each layers property to see if it is 'undefined'. If undefined, then define it. If the files have a defined coordinate system, but they are far apart, then they have been defined wrong.

If you want two files with a defined coordinate system to be in the same coordinate system, then you use the Project tool, not the Define Projection tool

Define Projection vs Project.... a visual guide

Re: Homogenisation

TheresaFurness — Thu, 27 Apr 2017 09:59:33 GMT

Many thanks, firstly. They are far apart, so shall try and investigate in ArcCatalog to see which one has been defined wrong

I look forward to reading your blog too, since I am now totally confused!

Terri

Re: Homogenisation

JayantaPoddar — Thu, 27 Apr 2017 11:09:05 GMT

Could you attach the screenshot showing the spatial extent of the projected layer (Layer Properties > Source tab)?

Re: Homogenisation

TheresaFurness — Thu, 27 Apr 2017 11:14:52 GMT

Hi,

The second layer :

Terri

Re: Homogenisation

TheresaFurness — Thu, 27 Apr 2017 11:18:28 GMT

Terri

Re: Homogenisation

JayantaPoddar — Thu, 27 Apr 2017 11:27:31 GMT

Is the data from Austria region? If you could attach a sample data from the projected data, I could have a look at it.

Re: Homogenisation

TheresaFurness — Thu, 27 Apr 2017 11:47:10 GMT

Have emailed it to you.

Thanks

Terri

Re: Homogenisation

DanPatterson_Retired — Thu, 27 Apr 2017 12:37:35 GMT

The first image is definitely in decimal degrees given its extent and its defined projection.

The second image is a strange one, given the extent values for the easting and the northing and the fact that the false northing is an extremely large negative number. Was that one defined as such already? or did you define it? since the northing values don't jive and given the latitude, I would expect something like a UTM since the northing is about 1/2 way to the N pole

Re: Homogenisation

TheresaFurness — Thu, 27 Apr 2017 12:41:38 GMT

I am a student of GIS - this was part of an assignment - the data was given incomlete like this to 'make us correct it' - but try as I may, I cannot work out that coordinate system either

Thanks anyway

Terri

Re: Homogenisation

DanPatterson_Retired — Thu, 27 Apr 2017 12:51:20 GMT

Well given the easting and northing values of the 2nd image, I think it is within the correct latitudinal range. The only thing to resolve now is what projected coordinate system would give rise to those values, hence my guess of some UTM or transverse Mercator based projection since 45 degrees is 1/2 way between the equator and the pole and the original definition of the metre was 1/10,000,000 of the distance between the equator and the pole... ergo, 5,000,000 metres-ish would be an appropriate northing. As for the easting, you should be able to figure what UTM zone you are in and whether your longitude falls to the east or west of the central meridian for the utm zone that covers the latitude and longitude range.

Of course this doesn't rule out any other projections that you might encounter in your studies that are unique or widely used in your area. Trial and error and/or comparison to a known dataset are your only options to narrow down appropriate candidates.

Re: Homogenisation

JoeBorgione — Thu, 27 Apr 2017 13:02:28 GMT

Try this: add one of the layers to an ArcMap session, right click and Zoom to Layer. In another ArcMap session do the same thing with the other layer. If one of them 'dissapears' from your screen, that's the problem child and it has an extent problem.

Re: Homogenisation

JayantaPoddar — Thu, 27 Apr 2017 13:21:26 GMT

Thank you for the mail. The correct projected Coordinate system for LULC_NAWI is WGS_1984_UTM_Zone_33N.

Go to the Shapefile Properties from ArcCatalog > XY Coordinate System Tab. And define WGS_1984_UTM_Zone_33N as the coordinate system.

The Project_area and LULC_NAWI will then exactly overlay on each other.

Re: Homogenisation

TheresaFurness — Thu, 27 Apr 2017 13:55:05 GMT

Excellent - that worked!

Please could you tell me how you ascertained that correct projected

Coordinate system - I hunted through my list for hours and tried MANY.

There must be an easier way.

Terri

Re: Homogenisation

JayantaPoddar — Thu, 27 Apr 2017 17:10:58 GMT

UTM is a very common PCS used globally. It was just a hunch.

Check How to calculate the UTM zone using longitude values (Decimal Degrees)

Re: Homogenisation

DanPatterson_Retired — Thu, 27 Apr 2017 17:13:05 GMT

plus your longitudes are in the appropriate range for that utm

Re: Homogenisation

TheresaFurness — Fri, 28 Apr 2017 04:44:09 GMT

Thanks - a very helpful link.

Terri

Re: Homogenisation

AnaPavcec — Wed, 27 Nov 2019 14:08:48 GMT

Hi,

I am also new in GIS.

How do I know name for the EPSG 31258 projection?