GPS Data Accuracy

[AdamkT1]

I am developing a program to receive GPRMC strings from gps receiver and am trying to use it for guidance.

I am concerned with the accuracy of data received. I shall explain my problem by an example:
For LAT , I recieve a string value of 4916.5892. This value actually is extracted from a long sentence. This value represents actual Latitude coordinate multiplied by 100. In actual the coordinates are 49 deg, 16 Min and about 35Sec.

I convert the string to double using atof and then divide the value by 100 to get the coordinate.

One second movement corresponds to about 31 meters and 1 sec= 1/3600=0.0002degrees.

Has anybody worked on this type of problem.

I shall appreciate any suggestions on how to increase the accuracy without using the DGPS and etc.

One logical answer is, it depends upon the GPS being used, any other answers...

Thanks.

[Douglas Kennedy]

The issue is with the representation of numerical values within the PIC by float. In decimal terms float is good for 6 significant decimal numbers may be 7 for certain values. No matter how precise your input float can not give you say more than 6 significant digits so your accuracy will always be of the order of one second of arc. I would parse out the degs and mins from the string and store them as integers. The seconds and decimal part of the seconds could go to your float if you choose. With the degs and mins handled separately you have 4 additional significant digits for your seconds( actually a fraction of a minute) so a float could represent nn.dddd of seconds two more significant digits than your input supplies.