**Course Generator > FAQ**

# How to choose the speed/slope curve?

Unfortunately there is no simple answer. It will depend on you. At first you will overestimate or underestimate your abilities but in time you will find the right settings.

The choice of curve will depend on the length of the course. Select the speed you would have if you speak with someone. It’s a speed that comes automatically. For me, it’s 10km/h. This method is a good starting point.

# Is it possible to generate a speed curve from a GPS record?

Yes! If you think a GPS record matches your level then follow the procedure below:

- Open the GPS file. It must contain the temporal data.
- Do not ask
**Course Generator**for a calculation otherwise it will overwrite the temporal data - Go to the tab “Analysis> Speed / Slope”
- A green scatter plot appears. These are the speed records according to the slope at each point of the track
- The red curve is the curve “Speed / slope” deduced from the scatter plot
- Click on the blue save icon
- Enter a name and a comment.
- Go to the “Speed / Slope” curve editing dialog and select the curve generated by the name you gave it. If necessary you can change its shape.

# The total distance is wrong!

**Course Generator** ne filtre pas les points GPS. Si vous avez beaucoup de points GPS par rapport à la distance (par exemple 1000 points pour 15km) alors l’erreur de positionnement du GPS entraîne une erreur de calcul.

**Course Generator** does not filter GPS points. If you have a lot of GPS points relative to the distance (eg 1000 points for 15km) then the GPS positioning error causes a calculation error.

The image below shows a view from above of a displacement. In blue, the actual displacement. In red, an example of recording made by the GPS.The higher the density of points, the greater the distance calculation error will be. More informations on GPSVisualizer.

In addition, **Course Generator** takes altitude into account when calculating the distance. So errors in the altitudes involve errors in the distance calculation.

Solutions :

- Use GPSVizualizer website to reduce the number of points (Advanced options > Max. points per track).
- Wait for
**Course Generator**to include a filter (in V4.1).

# The elevation loss or gain is wrong!

**Course Generator** does not change the altitudes and calculates the altitude difference using a filter set at 10m (variation before taking into account the altitude variation).

Les sites internet utilisent souvent les données SRTM afin de corriger les altitudes et calculer les dénivelés.

Websites often use SRTM data to correct altitudes and calculate elevations gain and loss.

The images below show the principle of operation.

The image on the left shows the actual record (red curve) of the altitude made with a GPS.

The right image shows the altitudes corrected with the SRTM data.

Solutions :

- Use GPSVizualizer website to correct the altitudes (Option : “Add DEM elevation data”).
- Wait for
**Course Generator**to incorporates a more efficient filter.