GeoCoordinates to Cartesian

Discussion of MicroSurvey CAD related issues and questions.

Moderators: Brian Sloman, Jason Poitras, James Johnston

GeoCoordinates to Cartesian

Postby MikeE » Thu Jul 15, 2004 10:26 am

Hi, I'm a newbie and have been trying to evaluate MS for use in a friends business. I have constructed a drawing and placed several buildings on it. How do I use the origins to convert geo coordinates captured with a GPS to the cartesian coordinates (Northing Easting Points) in my drawing.

Thanks,

Mike
MikeE
 

Postby Scott Partridge » Thu Jul 15, 2004 1:32 pm

Mike, this may or may not be simple depending upon a number of issues:

Where do the geo coordinates come from and how accurate are they? There is a big difference in the accuracy between GPS data from a consumer grade handheld to a survey grade RTK system.

Have the GPS coordinates been verified as correct? What datum are they referenced to (NAD83, NAD27, etc)

Do you have known grid/ground coordinates for any of the GPS points or were you going to assume a user defined coordinate system?

When you talk about grid coordinates (N, E) are you talking about mapping grid or 'ground' coordinates (ie what you would measure with a total station)

Remember that you are trying to fit data from a curved surface to a flat plane, so there will be some distortion.

Are mean sea level elevations required?

These are just the questions off the top of my head without putting much effort into it. There are probably others.
Scott Partridge
 
Posts: 35
Joined: Sun Nov 10, 2002 11:44 am
Location: Calgary, Alberta

Geo to Cartesian

Postby MikeE » Thu Jul 15, 2004 2:27 pm

Hi Scott,

Thanks for the reply. I'll try to answer best I can.

Where do the geo coordinates come from and how accurate are they? There is a big difference in the accuracy between GPS data from a consumer grade handheld to a survey grade RTK system.

Understood. At the moment, it is a consumer grade GPS. We were trying to find out how easy this was to do in MS.


Have the GPS coordinates been verified as correct? What datum are they referenced to (NAD83, NAD27, etc)

No, WGS84

Do you have known grid/ground coordinates for any of the GPS points or were you going to assume a user defined coordinate system?

User Defined

When you talk about grid coordinates (N, E) are you talking about mapping grid or 'ground' coordinates (ie what you would measure with a total station)

Mapping

Remember that you are trying to fit data from a curved surface to a flat plane, so there will be some distortion.

Also understood.

Are mean sea level elevations required?

No.


Thanks again for the help.

Mike
MikeE
 

Postby Guest » Fri Jul 16, 2004 5:27 am

Another question Mike, akthough you have already simplified it a great deal.

When we are talking about a mapping grid, do you mean a defined grid like UTM, SPC etc with predefined projection parameters or are you talking about an arbitrary user grid where you assign assumed coordinates to one of the points, ie. 5000.00 North 5000.00 East and an assumed orientation (North direction)?
Guest
 

Geo to Cartesian

Postby MikeE » Fri Jul 16, 2004 10:02 am

Arbitrary.

Thanks,

Mike
MikeE
 

Postby ianw2 » Fri Jul 16, 2004 12:18 pm

What's the purpose of your exercise? Do you have the lats/lons on screen? How did you collect them? What is the tolerance of the collected points? What are your credentials? What is your level of experience with surveying? Mapping? GPS?

If you’re using a hand-held unit, you’re only going to have points that are within 0.5 meters of true IF you are using a unit with a broadcast correction from a subscription service. If your unit isn’t tied to a subscription service, you’re only going to get 10 meters accuracy.

Hand-held units are not designed for surveying. They’re designed for getting you within 10 meters of where you want to be. The kind of topographic survey you describe is something that a surveyor does and keeps accuracies within a few centimeters.

What you are proposing could be very dangerous and potentially carries a high degree of liability. In California, it might even be construed as “Adding and Abetting”, a misdemeanor punishable by suspension of license!

Please give us a lot more details before any of us who are licensed would dare answer.
Ian Wilson
Ian Wilson Land Surveying, Inc.
Temecula CA 92591
(951) 684-1044
ianw2
 
Posts: 139
Joined: Sun Nov 24, 2002 6:45 am
Location: Temecula, California

GPS

Postby Glen Cameron » Sun Jul 18, 2004 7:28 pm

In general, if you can create a coordinate ASCII file and read it into MSCAD, we can do something with it. If the file was collected in Lats and Longs, then you can import that as well.

Conversions - now this is where we may or may not be able to automate the process. If you were converting UTM type coordinates from one datum to another, then we have routines to do this under the MsPoints menu -> Geodetic. If you are simply applying a Grid to Ground scale factor then you would need to simply run the scale. move and/or rotate commands to manipulate the points to match the system you are using locally on the job.

Others have addressed some of the issues you may need to consider in collecting your data and legal issues, etc. But if you wish to import the data and use it, we can work with you on this.

Cheers,
Glen W. Cameron, C.E.T.
City of North Bay, Ontario
Glen Cameron
 
Posts: 1395
Joined: Fri Nov 08, 2002 12:18 pm
Location: Corbeil, Ontario, Canada


Return to MicroSurvey CAD

Who is online

Users browsing this forum: No registered users and 2 guests

cron