How to use iCMTGIS III to check GPS accuracy
February 3, 2017 Leave a comment
“I have purchased the iCMTGIS III and I am using a TIFF image as a background map. I am having problems with the GPS not very close to a known point. Do you have any suggestions? I am using a Bad Elf Pro+ as an external GPS it says it is supposed to have 3-5 meter accuracy. Do you suggest another GPS? Is there only one place to change coordinate system or is there other parameters that may need to be changed to get acceptable accuracy?”
Does your iPad come with GPS? Perhaps the iPad is using its internal GPS, which has poor accuracy. Please turn off GPS from all the apps on your iPad. Then, with the Bad Elf Pro+ connected to your iPad and turned on, run iCMTGIS III and select GPS – Turn on GPS.
Another way to ensure that the iPad uses the external GPS is to turn on the Airplane mode under the iPad Settings. For details, please see our blog post at:
To check the accuracy of the GPS receiver against the LLA coordinates of a known point or survey mark, you could first create a Point Topic then add a Point by using the Add Point by Coordinates function from the Tools menu. Enter the latitude and longitude of the known point. With the Bad Elf GPS having been turned on for a few minutes, check the location of the GPS marker against the known point. The published accuracy is an average value.
To record a Point Feature, please use GPS – Collect and log GPS point data for 5 minutes or longer. The app will compute and display the average point position. Measure the distance between the recorded point and the known point.