When I connect DroidPlanner with my APM to ArduPlane (via USB telemetry), the reported altitude on HUD is not correct, is display like 48 meters.
Is any way to reset this altitude?
When I am using MissionPlanner (instead of DroidPlanner), the HUD altitude is correct.
Usually when I am using MissionPlanner on laptop, I am using PreflightCalibration, which reset the altitude to correct value.
I have the EXACT same issue. Do you have amp 2.5 with a mediatec [?] gps? In older MP I can simply reset to zero. With newer MP and Droidplanner I can’t do this. the firmware on the apm 2.5 is about 8 months old. vs 2.72
Are you guys aware that both MP and DP use Altitude above Sea Level by default?
Those 48m is the height about see that you are currently at your location. Here is a great video (with some info that Im sure you havent seen before):
youtube.com/watch?v=q65O3qA0-n4
Above see level… yes that is the problem. It reads zero until the gps lock then it says 240 feet or so. That might be what it is above sea level but how high it is off the ground where it was armed is what I need to see. I can zero the home alt on a older MP and I just got lucky I guess with andropilot for some reason it just starts at zero. I like DP better though but always doing the math in my head with my math skills is dangerous! 
I wish there was a ‘reset home alt to zero’ .
The new version of droidplanner (v2) shows the altitude as relative to home. Could you give it a test an report back here?
I re i stalled this version
github.com/DroidPlanner/droidpl … v2.0.0_RC1
But unfortunately it does the same thing. It reads 209 m after a gps lock. It also has a strange issue with overlapping some other numbers. see pic.
I love the editor and overall look and feel of the apm it’s really nice! You can tell a ‘pilot’ is writing this.
Update
I just got my brand spanking new Pixhawk!!! YEA!!! Anyway it seems to work flawless with DP including no problem with the altitude. It reads zero on start no problem. It also feels COMPLETELY stable!!! I have had it quit a few times before but I have come to find out it’s related to the USB telemetry not being associated with DP within the tablets droid OS right. NOT DP. A simple fix… just pull the usb… plug it back in. But I digress… regarding DP and the altitude it is NOT a problem for me anymore. I really think the issue has always been with my particular build of APM 2.5. Not any software. Also I had another issue the mode would not change on the screen when I flipped the switch on my TX. It does now. Great job this is by far the best base station software out there in my book. 
Thanks Arthur and to all working on this!!!
one more thing… the firmware on my apm 2.5 was over a year and half old. My plane flew so perfect I never updated the firmware. So that alone could have been the issue and has since been corrected.