Inserting GPS points on ACAD2000 from a GPS reciever

[gpinel]

I am trying to add GPS waypoints from a handheld GPS reciever to a scaled cadastre based map on AutoCAD2000.

I have found one software package that will do it, at http://www.aztechsoft.com/gpscad.htm
but was wondering if there are any other options out there.

Also i found that it did not insert the points where they should be, even though the scale was correct. Moving the points to the correct location fixed this (using a few control points and moving the lot relative to these), but would prefer if they inserted in the correct positions to begin with.

[CADTutor]

Well, you could probably do the whole thing yourself. Since the waypoint file is just a database, you could convert this to a simple txt file and then write a LISP routine to read this file, make the conversion from Long/Lat to X,Y and then draw the points in AutoCAD but it seems quite a hassle when this software will do it all for you.

I notice that there is an option to shift all drawn points to a user specified location using the software. I guess you must be using the free trial version. I suggest you have a bit more of a play around with it before looking for alternatives. On the face of it, it looks as though it ought to do just what you want. I don't think $325 is too much to ask for something that could be a great timesaver.

[SpeedCAD]

I am trying to add GPS waypoints from a handheld GPS reciever to a scaled cadastre based map on AutoCAD2000.

I have found one software package that will do it, at http://www.aztechsoft.com/gpscad.htm
but was wondering if there are any other options out there.

Also i found that it did not insert the points where they should be, even though the scale was correct. Moving the points to the correct location fixed this (using a few control points and moving the lot relative to these), but would prefer if they inserted in the correct positions to begin with.

Hola...

No entiendo nada de GPS, pero si logras pasar los puntos a Excel podras graficarlos con el programa ExCoorCAD2004, entra a la siguiente pagina:

http://speedcad.webcindario.com/excoorcad/excoorcad.htm

[billsta]

just wondering, can't we just record the way points and then plot it in CAD i presume most of us draw in 1:1 scale anyway...

but than again, wouldn't that also depends on you GPS accuracy as well??

been ponding on this for a while, be good to guess site conditions...

[Mr T]

Well, you could probably do the whole thing yourself. Since the waypoint file is just a database, you could convert this to a simple txt file and then write a LISP routine to read this file, make the conversion from Long/Lat to X,Y and then draw the points in AutoCAD but it seems quite a hassle when this software will do it all for you.

I would post this across to Fuccaro (great chief of the LISP clan)

Nick

[fuccaro]

It sounds to be possible. But I have no idea about the structure of that file. Maybe you do not need lisp if you can import the coordinates in Excell. They are ways to transfer points from excell to AutoCAD and draw a polyline using that points.

[gpinel]

The file format from the GPS2CAD program comes across as a txt file and two waypoints in the file looks like this, the waypoints are just repeated to form a collection of points with a few extras attached:

GHOME,-27.49910,152.98322,0.0,21-JUN-03 09:11,HOUSE
RCM,-26.45748,151.97827,0.0,20-JUN-03 00:24,FLAG

where GHOME and RCM are the names of the waypoints, the next two numbers are lattitude and longitude, then altitude (currently 0.0m), date, time and HOUSE or FLAG are the types of symbols for the points stored in the GPS reciever.

I can get these numbers into excel, but would think they would have to be converted to UTM format (Northings and Eastings - metres rather than degrees) to plot the points in autoCAD properly. There are spreadsheets that can do this, but i guess this is all starting to get a bit complicated, isn't it?

[fuccaro]

So do you have a lot of lines like this two and we need to extract the coordinates from, right? And those coordinates must be transformed in XY coordinates and transferred on the screen for draw a polyline trough, is it correct?
Do you have a formula to transform the coordinates returned by the GPS from lat-long format? I could find-out the way to transform them using the radius of the Earth. But I am sure that people working daily with this things can tell me the right way.
I need to have confirmed if I understand correctly the problem because I seen GPS only on the TV. And I have problems with my English too.
Cheers!

[gpinel]

For a great (Australian) site on GPS calculations see:

http://www.ga.gov.au/nmd/geodesy/datums/calcs.jsp

Especially the MS Excel spreadsheet which computes a similarity transformation (and converts between geodetic coordinates and Earth-centred Cartesian coordinates). (latitude, longitude, ellipsoidal height <-> X Y Z)
The rest of the site is pretty informative too...

All I am really interested in is transferring single points onto CAD, and these spreadsheets require each position be entered one at a time - time consuming and error prone!!
I am still unsure how to transorm these points onto a CAD drawing once i have them in cartesian coordinates, any hints?
and fuccaro - your English is perfect!

[fuccaro]

Here is my attempt. I copied things I do not understand so I preserved in the lisp the names of the Excel cells to make the program easy to debug. This is not a good style but I usually work with bearings and screws not with maps and GPS devices. Gpinel (and everybody) please try the routine and send me your feedback. Thanks.

; import co-ordinates from a GPS device
; mfuccaro@hotmail.com
;----------------------july 2003-------
;
(defun c:gps( / oldecho LayText LayPoint Texth file fline points i ch x1 y1 z1
	     d9 d13 d14 d15 d16 d17 h7 h8 i7 i8) 
  (setq oldecho (getvar "CMDECHO"))
  (setvar "CMDECHO" 0)
  (setq d9 749.671 		;* elipsoidal height
	d13 6378160.0  		;* Semi major axis (a)
	d14 298.25		;* Inverse flattening (1/f)
	layText "text"		;* layer name for text
	LayPoint "points"	;* layer name for points
	texth 75000		;* height for text
	file (open (getfiled "Find your coma delimited text file" "" "txt" 0) "r")
	fline (read-line file))	; FLINE = a line from the file
  (while fline
    (setq i 0 point nil)
    (repeat 3
      (setq ch "")
      (while (/= ch ",") (setq i (1+ i) ch (substr fline i 1)))
      (setq point (cons (substr fline 1 (1- i)) point)
	    fline (substr fline (1+ i)))
      )
    (setq point (list (caddr point)
		      (atof (car point))
		      (atof (cadr point)))
	  fline (read-line file)
	  h7 (cadr point)		;latitude
	  h8 (caddr point)		;longitude
	  i7 (/ (* h7 180.0) PI)
	  i8 (/ (* h8 180.0) PI)
	  d15 (/ 1.0 d14)
	  d16 (- (* 2.0 d15) (* d15 d15))
	  d17 (/ d13 (sqrt (- 1.0 (* d16 (sin i7) (sin i7)))))
	  x1 (* (+ d17 d9) (cos i7) (cos i8))
	  y1 (* (+ d17 d9) (cos i7) (sin i8))
	  z1 (* (+ (* (- 1.0 d16) d17) d9) (sin i7)))

    (entmake				;writing the points name
      (list
	(cons 0 "TEXT")	(cons 10 (list x1 y1 z1))
	(cons 40 texth)	(cons 8 LayText)
	(cons 1 (car point))))

    (entmake (list			;creating the point
	   (cons 0 "POINT") (cons 67 0)
	   (cons 8 layPoint) (cons 10 (list x1 y1 z1))))
    )					;while fline
  (close file)
  (command "zoom" "e")
  (setvar "CMDECHO" oldecho)
  (princ)
)
(princ "\nProgram loaded. Type GPS at the command prompt.")
(princ)