Document MODIS data sampling

[yellowcap]

Added Modis to our training data set using stacchip.

• Chip dates and locations data added to general index using the new modis processor in stacchip
• All data prechipped using the slightly adapted prechp module
• Stats computed using 10% of the data through the almost unchanged stats module

Most of the work went into finding a reasonable projection for the data, which comes in SIN grid originally. The processor reprojects the modis tiles into web mercator. The prechipping and stats were working almost out of the box 🚀 .

[brunosan]

@yellowcap can you share more about the projection choice? From what I remember we do not reproject in other cases, correct?

[srmsoumya]

@brunosan Based on my discussion with Daniel, default projection of MODIS had a lot of empty pixels, so he had to reproject them into Web Mercator & slice to areas that are best available. Yes, we don't reproject any other data source.