Coordinate help

[John316]

Okay, here is my latest question.

I am importing elevation data as a .dxf .xyz or .shp.

If I remember correctly, Irricad uses state plane coordinates, correct? I am trying to figure out how to correlate between the state plane cords, and the typical geographical lat/long that Google Earth uses. Here is why. I import my elevation data. Then I need to figure out where my field is. Can somebody shed some light on how that works?

Let me know if there is anything else that I can help explain. I will do my best.

Thanks for the help.

John

[Dan Crosby]

Hi John,

Converting lats/longs to planar coords can be a tricky business and can depend on the projection type you want/have to use, and where the reference point is for your area of the world. However, if you are using Google Earth I'd suggest using the Universal Transverse Mercator (UTM) system - because that is built in!

In Google Earth look under Tools|Options... Show Lat/Long - you can select UTM there, and the lats and longs will be 'planarised' to the correct UTM zone.

For instance, our office is at 43°38'43.89" S 172°28'03.43" E or UTM Zone 59 618364.64m E 5166481.03m S. If you use these coords you can swap between Irricad and the 'real world' with ease. If you do use them though, I'd suggest making use of Irricad's grid user origin capability (Settings|Grid/Origin) to make the numbers more managable.

You can find out more about UTM here:
http://en.wikipedia.org/wiki/Universal_ ... ate_system

Hope this helps,

Dan

[John316]

Dan,

Thank you for the reply. I will do as you suggest.

However, that will be a tough transition for me. Could I submit a suggestion for Irricad to be able to read geographic cords? I know that would be very helpful to me.

Thanks.

John

[Dan Crosby]

John,

Irricad can import SHP and text file (CSV, XYZ) lat/long data in the UTM WGS84 projection, though this requires the data to be in decimal degrees (this is also available in Google Earth).

What format is your data in?

Dan

[John316]

Right now most of my data has been .dxf files.

So are you saying that IC has the ability to use regular geographic cords? And the cords are based on what the original file's cords are?

Thanks for your help.

John

[Dan Crosby]

John,

No, sorry for the confusion. Irricad can import data in lats/longs but will convert it to planar coords.

So, your suggestion would be for Irricad to be able to work generally in geographical rather than planar coordinates?

Dan

[John316]

Dan,

That is correct. My suggestion is for Irricad to be able to work in geographical coordinates. Ideally it would be an option.

Thanks.

John

[jimmylee63]

Hi Dan,

I need to know if Google Earth or anyother web based resource has elevation data available as well as Long. & Lat. Can you help?

[Dan Crosby]

Hi Jimmy,

Google Earth does have elevations, but they are difficult to extract directly from there. There are based on SRTM data and probably won't be accurate enough for your purposes.

You can also get elevation data from USGS, which is more accurate than the STRM dataset. This still may not be good enough depending on the relative accuracy (more important than absolute accuracy) at the location you are interested in. For instance, you can get USGS derived elevations for Washington State here:

http://gis.ess.washington.edu/data/rast ... index.html

Failing the above, you would have to rely on local surveys - which would more than likely end up in AutoCAD format, or buy data from a company such as Intermap. The Intermap dataset is very new and very accurate, but obviously, it comes at a cost.

Hope this helps,

Dan

[Matt Binder]

If I could also make comment on the use of Google Earth, we have found that the elevation data can be more than 10m out and is not always relative in accuracy.

In my experience I would not suggest using any "free" means of obtaining elevation data as there is no guarantee of it's accuracy.

[jimmylee63]

Matt & Dan,

Thank you for the information.

I will go to Intermap and sign up. It may cost but there could be some savings in an online purchase versus the time and travel costs.

Thanks again,

Jim Fowler
Dunning Irrigation

[Kosi Kalogerinis]

If I could also make comment on the use of Google Earth, we have found that the elevation data can be more than 10m out and is not always relative in accuracy.

In my experience I would not suggest using any "free" means of obtaining elevation data as there is no guarantee of it's accuracy.

In addition, we have also found google earth site dimensions can also be inaccurate somewhat.