Double xovers found - No xovers found

[wdesprats]

Using the altimetry data available in: https://www.dropbox.com/s/iptb3j6sncibcyu/xov_test.tar?dl=0

One can find in total 4 xovers between the 4 ground tracks (e.g., in the northern hemisphere), but these 4 xovers should results in 2 unique xovers. Moreover, one xover is missing (see

• 2 xovers found between CALASIMRDR3105011057.TAB and CALASIMRDR3105090518.TAB
• 2 xovers found between CALASIMRDR3105010813.TAB and CALASIMRDR3105090233.TAB
• 1 missing xover between CALASIMRDR3105010813.TAB and CALASIMRDR3105090518.TAB

[steo85it]

Thanks for the working example, will work on it and let you know!

[steo85it]

My initial check got the code finding 4 rough xovers:

   xOvID        LON        LAT        orbA        orbB  mla_idA  mla_idB
0      0  40.991457  65.504032  3105010813  3105090518   313919  1086232
1      1  42.127041  69.837094  3105010813  3105090233   315113   986369
2      2  39.648267  70.141551  3105011057  3105090518   413847  1084965
3      3  40.766980  73.106953  3105011057  3105090233   414666   985603

and 3 fine xovers (the one at lat~73N is excluded, not exactly sure why yet). However, I couldn't find those double xovers you have been mentioning...

[steo85it]

About that missing xover ~73N, there seems to be some issue in either reprojecting between rough and fine xov search, or something else causing a difference of 20km between the 2 tracks: as opposed to a more typical configuration like this one: This causes the xover not to be detected, but I'm not yet sure why. All other xovs look fine for me.

[wdesprats]

I checked again, more thoroughly this time, and there are indeed no double xovers ...I actually plotted the xover on each ground tracks. The differences between the two points were coming from the numerical differences when computing the lat/long from the time of the first ground track, and the time on the second ground track. But the two points actually comes the same xover. Sorry for this unnecessary check...

[steo85it]

Ok, thanks for confirming and no problem, there is anyway an issue with the missing xover that it would be good to solve.

[steo85it]

is this still an active issue?

[wdesprats]

I found out some crossovers were excluded because during the rough search, at least two intersections were found. In the image below, one can see an intersection is clearly off.

I'm not sure what is the reason why the intersection function is finding wrong intersection, but in a future update, in case more than one intersection is found, a safety check would be added to remove wrong intersection, in case their distance from each ground tracks is more an 10x the mean sampling distance.

In case more than one intersection is found, a warning message will be displayed, and the associated ground track combination will be excluded.

[wdesprats]

The variable checked for the find of a rough xover was not reinitialized at the proper location. The previously found xover was appended to the list of found xovers until a new xover was found, leading to duplicates in the final list of rough xovers.