Combo Maps

[Cilantro13]

Scott:

New version is great, and discovered that a little editing for each GPS file is in order to get rid of the points as it calculates the elevation in the elevation profile.

Three questions:
1. What have people found to be the most accurate measurement of elevation. I like DEM because it goes straight from the map data, but is it really the most accurate? If so, what settings provide the most reliable results with respect to total elevation gain?

2. With one track, I just noticed my stopped time was excessive. I rode two hours, with a about 15 minutes of stopped time for a flat. But the track showed 3 1/2 stopped hours. So I went into the track properties to look at the raw data points... I discovered that it actually showed three tracks, with the first two were at my house (listed as tracks 1, 2, and 3). But the points corresponding to my house didn't show up on the map, only track 3, which was the moving track did? Any ideas what is going on because it would a lot easier to delete the spurrious points from the map than looking at raw data. (BTW, I love that it is so easy to see the data points and edit them when necessary)

3. (MAIN QUESTION) What is the reason that you cannot select Color Aerial or Landsat in the combo maps. I would really like to have an option to select Color Aerial and Topo, with the topo set at 20% (that way you can see the contours if you focus, but you aren't limited).

If possible, may I request this as a feature request?

Thanks.

[ScottMorris]

1. Depends on your GPS, and how good sky / blockage conditions were the day you recorded the track.  Remember that if you have bad 2D errors in your track, you'll get incorrect DEM elevations, especially in steep terrain.

2. What GPS are you using?  You may be able to eliminate those useless tracks before saving them out upon download.

3. Those maps are in a different projection type.  But TF is moving towards that projection type -- we definitely intend to add support for color aerial / topo / landsat in combo mode.

Thanks for posting.

[Cilantro13]

Thanks for the reply Scott:

Using a Garmin eTrex Vista. In this case, I had actually overrun the track memory with subsequent rides -- so I took the track from my SD card. Now that I think about it, I'll bet that was the problem. I wonder if I correctly reset the track data prior to the ride, but still weird why it wouldn't show up on the map. hmmm.

I just double checked the file -- turns out it did show up on the map. I just didn't pay close enough attention.

Thanks again.

Cheers,

Marlan Walker

[Larry]

Scott:
1. What have people found to be the most accurate measurement of elevation. Thanks.

Hi Marian, 
For what it's worth, here is my experience, adding to what Scott said: if I remember correctly, the best res on the DEM model is a point roughly every 100 feet. That in itself can lead to a significant error. In general, here in the NW, my guess is that plus / minus 50 ft is the best the DEM can do. Sometimes it's much worse. On the other hand, when the GPS gets a good, unobstructed view of the sky, I've been amazed at the accuracy. On many of the peaks in the Cascades where where I have compared the elevation reported by the GPS to the transit elevation, or the elevation of a benchmark, I often get agreement within five feet! This even though the GPS says that the best it can do is say 12 feet.  On the other hand, in deep forested valleys, the GPS elevation data can be near worthless. One clue to this in the field is noticing that the GPS elevation data lags. (That is, when you arrive at a point of known elevation, the
GPS reports the elevation you attained  earlier.)

Hope this helps,

Larry

[Cilantro13]

Thanks Larry. At the end of the game, I suppose getting a value for your total climb is something of a shell game... Especially the longer you go, the more varied the readings to total elevation get due to error over time. Hmmm, I suppose that I will just stick with GPS elevation (mine calibrates to barometric pressure).

Marlan