Running Monocular Visual Simultaneous Localization example distance as covered by vehicle equip with camera and gps is very less as ground truth data on custom dataset images

Hi

I am using matlab example Monocular Visual Simultaneous Localization and Mapping. When i run this example on my custom data set by creating own bag fo features and other necessary tuning, the distance it covered is very less "distance travel in z direction". I have my gps reading which shows 50 meter distance travelled. Can some one please point out the paramter which i need to consider for estimating correct pose.