Thanks for all the info Arnold. I will study all these links ASAP. I had a Garmin 12A (many years ago) that gave the actual height close to the survey value of 928M ASL. I wonder if those calculated the real values..
>Raj, > >don't trust the height asl from (older) maps. There are so many different >local >sea level definitions around the world, which are not yet WGS84/ EGM96 >conform (WGS 1972 would be good as well)! >I had similar problems comparing swiss and and german map values >with the Shuttle Radar Topography Mission (SRTM 2000) values. > >On http://www.colorado.edu/geography/gcraft/notes/datum/edlist.html >I found interesting informations about the differences (tables). >Eg. India used the Everest ellipsoid (India 1956, for Inda and Nepal) >where the differences to WGS84 are (d = delta): >dX= 295, dY= 736, dZ= 257 meters, what might explain already some >discrepancies. Attention to the horizontal displacements as well! > >So nothing to worry, as already correctly explained by several other >fellow Time Nuts, use the elevation found with the auto position function >in LH, this is the right GPS value for this purpose ( perhaps moving around >up to 1 m or similar), which is of no concern I think. Mark Sims and >John Miles did really a good job! >(The self survey function in Thunderbolt Monitor does give a similar >result with somewhat less resolution/ precision.) > >Searching around I found another page with good informations for >beginners: 'Datum of a GPS Receiver' >http://homepages.slingshot.co.nz/~geoff36/datum.htm > >The therein mentioned calculator >'Geoid Height Calculator NGA EGM96', url: >http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm96/intpt.html >does give the same results... > >enjoy the time > >Arnold, DK2WT > >On Thu, 11 Feb 2010 06:26:42 +0530, Raj wrote: > >>My GPS reading is about 850 +- 1 >>The "official" height ASL = 920 > >>This calculator gives me ~936 > >>So what should I use ? > >>Thanks >>Raj > >>At 10-02-10, you wrote: >>>Try to find your correct height here: >>>http://sps.unavco.org/geoid/ >>> >>>If you put in your correct coordinates without any input for the elevation, >>>you will get theorthometric height, which is the GPS ellipsoidal height >>>minus geoid height. That is the amount you need to subtract from >>>your Thunderbolt GPS height in order to get your local geodetic height >>>(WGS84). >>> >>>Filling in the Thunderbolt GPS height you will get the 'real' height >>>for your antenna... >>> >>>Some explanations: >>>http://www.unavco.org/edu_outreach/tutorial/geoidcorr.html >>> >>>On my location I have always to reduce the GPS height by 46.623 m. >>>Good luck with TB and the Lady Heather, >>> >>>Arnold, DK2WT >>> >>> >>> >>>On Wed, 10 Feb 2010 14:20:36 +0100, EB4APL wrote: >>> >>>>Raj, >>> >>>>Ask them about ellipsoidal and orthometric heights, or the local >>>>difference between the geoid and the WGS84 ellipsoid. Also your long >>>>and lat may change depending of the Geodetic Reference System chosen. >>>>By default GPS receivers use WGS84 and ellipsoidal height. >>> >>>>73 de Ignacio, EB4APL >>> >>>>-------------------------------------------------------------------------------------- >>>>Raj wrote: >>>>> Thanks Stan, >>>>> >>>>> That worked, I did not see the control menu properly! >>>>> >>>>> I set the co-ords to 0 0 0 and started survey. The Tbolt found the Lat >>>>> long withing a few minutes and only the altitude is about 70 M below the >>>>> official figure for my place. I live a a few hundred meters from >>>>> Bangalore center and I am at the same height.. must check with the survey >>>>> dept. down the road!! >>>>> >>>>> 73 >>>>> Raj vu2zap >>>>> >>>>> >>>>> At 10-02-10, you wrote: >>>>> >>>>>> Hello Raj, >>>>>> >>>>>> using the trimble T'boltMON software: >>>>>> >>>>>> Start with a "factory reset" in the control menu >>>>>> >>>>>> follow previous guidance of enabling the "save position" capability, >>>>>> >>>>>> Then to restart a survey >>>>>> >>>>>> go to the control menu (on left), >>>>>> select "restart self survey" >>>>>> >>>>>> >>>>>> In lady Heather V3.0 beta of 21 Jan '10 ( available from the KE5FX >>>>>> website): >>>>>> keyboard enter a "s", for survey >>>>>> then "s" for a standard survey, >>>>>> use the default of 2000 samples, for a start >>>>>> Then "enter" >>>>>> >>>>>> Time for me to go to bed. >>>>>> >>>>>> Please advise of progress. >>>>>> >>>>>> Stan, W1LE >>>>>> >>>>>> >>>>>> Raj wrote: >>>>>> >>>>>>> Thanks Stan, >>>>>>> >>>>>>> I did that but I can't where to "start the survey" in TBolt. In lady >>>>>>> heather there >>>>>>> is a key for it. >>>>>>> >>>>>>> At 09-02-10, you wrote: >>>>>>> >>>>>>> >>>>>>>> Hello Raj, >>>>>>>> >>>>>>>> that location is probably where the coordinates were last saved. or >>>>>>>> there abouts.... >>>>>>>> Or those are the default factory settings from memory, >>>>>>>> and new coordinates were never saved. >>>>>>>> >>>>>>>> redo the survey and save the results. >>>>>>>> >>>>>>>> using T'boltMON V2.60 on a PC: >>>>>>>> >>>>>>>> go to menu "set up", then "self survey", click on the "save >>>>>>>> position flag" >>>>>>>> then "set survey", >>>>>>>> then "save segment", >>>>>>>> then "close" >>>>>>>> >>>>>>>> redo the survey and afterwards verify the local coordinates were saved. >>>>>>>> >>>>>>>> Lady Heather (software) can also be utilzed for these functions. >>>>>>>> >>>>>>>> Any problems, please advise. >>>>>>>> >>>>>>>> Stan, W1LE >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> Raj wrote: >>>>>>>> >>>>>>>> >>>>>>>>> Can someone point me to info that would clarify why my Tbolt's >>>>>>>>> self survey puts my house (AFAIK ~920M ASL, 13N 77.35E) in the >>>>>>>>> Pacific ocean, south of Vancouver and west of Seattle and about 10 >>>>>>>>> meters under water. I am doing something wrong for sure! >>>>>>>>> >>>>>>>>> My sons iPhone gives me right co-ordinates but it's way off the >>>>>>>>> altitude. >>>>>>>>> >>>>>>>>> Regards >>>>>>>>> >>> >>> >>> >>> >>>_______________________________________________ >>>time-nuts mailing list -- [email protected] >>>To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>and follow the instructions there. > >>-- >>Raj, VU2ZAP >>Bangalore, India. > > > > > >_______________________________________________ >time-nuts mailing list -- [email protected] >To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. -- Raj, VU2ZAP Bangalore, India. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
